using System;

using System.Collections.Generic;

using System.Linq;

using System.Numerics;

using System.Text;

public class Program

{

    public static void Main()

    {

        var res = MultiplyBigIntegers("9999910188888", "123456789").TrimStart('0'); 

        Console.WriteLine(res);

    }

    static string MultiplyBigIntegers(string leftIntAsString, string rightIntAsString)

        {

            if (leftIntAsString.Length > rightIntAsString.Length)

            {

                rightIntAsString = rightIntAsString.PadLeft(leftIntAsString.Length, '0');

            }

​

            if (rightIntAsString.Length > leftIntAsString.Length)

            {

                leftIntAsString = leftIntAsString.PadLeft(rightIntAsString.Length, '0');

            }

​

            int reminder = 0;

            string result = GetBigProduct(leftIntAsString, rightIntAsString, ref reminder);

​

            return (reminder.ToString() + result).TrimStart('0');

        }

​

        static int GetRightPart(string leftIntAsString, string rightIntAsString)

        {

            string a = leftIntAsString.Substring(leftIntAsString.Length - 4, 4);

            string c = rightIntAsString.Substring(rightIntAsString.Length - 4, 4);

​

            int aInt = Convert.ToInt32(a);

            int cInt = Convert.ToInt32(c);

​

            return aInt * cInt;

        }

​

        static string GetMiddlePart(string leftIntAsString, string rightIntAsString, ref int reminder)

        {

            if (leftIntAsString.Length < 4 && rightIntAsString.Length < 4)

            {

                leftIntAsString = leftIntAsString.PadLeft(4, '0');

                rightIntAsString = rightIntAsString.PadLeft(4, '0');

            }

​

            if (leftIntAsString.Length < rightIntAsString.Length)

            {

                leftIntAsString = leftIntAsString.PadLeft(rightIntAsString.Length, '0');

            }

​

            if (rightIntAsString.Length < leftIntAsString.Length)

            {

                rightIntAsString = rightIntAsString.PadLeft(leftIntAsString.Length, '0');

            }

​

            string a = leftIntAsString.Substring(leftIntAsString.Length - 4, 4);

            string b = leftIntAsString.Substring(0, leftIntAsString.Length - 4);

​

            string c = rightIntAsString.Substring(rightIntAsString.Length - 4, 4);

            string d = rightIntAsString.Substring(0, rightIntAsString.Length - 4);

​

            int fakeInt = 0;

            if (b.Length > 4 || d.Length > 4)

            {

                return GetBigSum(GetBigProduct(a, d, ref fakeInt), GetBigProduct(b, c, ref fakeInt), ref reminder);

            }

​

            int aInt = Convert.ToInt32(a);

            int cInt = Convert.ToInt32(c);

            int bInt = Convert.ToInt32(b);

            int dInt = Convert.ToInt32(d);

​

            int result = aInt * dInt + bInt * cInt + reminder;

            reminder = result / 10000;

​

            return (result % 10000).ToString("0000");

        }

​

        static string GetLeftPart(string leftIntAsString, string rightIntAsString, ref int reminder)

        {

            if (leftIntAsString.Length <= 4 && rightIntAsString.Length <= 4)

            {

                int aInteger = string.IsNullOrEmpty(leftIntAsString) ? 0 : Convert.ToInt32(leftIntAsString);

                int cInteger = string.IsNullOrEmpty(rightIntAsString) ? 0 : Convert.ToInt32(rightIntAsString);

​

                int product = aInteger * cInteger + reminder;

                reminder = product / 10000;

​

                return (product % 10000).ToString("0000");

            }

​

            return GetBigProduct(leftIntAsString, rightIntAsString, ref reminder);

        }

​

        static string GetBigSum(string leftIntAsString, string rightIntAsString, ref int reminder)

        {

            if (leftIntAsString.Length < 4 && rightIntAsString.Length < 4)

            {

                leftIntAsString = leftIntAsString.PadLeft(4, '0');

                rightIntAsString = rightIntAsString.PadLeft(4, '0');

            }

​

            if (leftIntAsString.Length < rightIntAsString.Length)

            {

                leftIntAsString = leftIntAsString.PadLeft(rightIntAsString.Length, '0');

            }

​

            if (rightIntAsString.Length < leftIntAsString.Length)

            {

                rightIntAsString = rightIntAsString.PadLeft(leftIntAsString.Length, '0');

            }

​

            string a = leftIntAsString.Substring(leftIntAsString.Length - 4, 4);

            string b = leftIntAsString.Substring(0, leftIntAsString.Length - 4);

​

            string c = rightIntAsString.Substring(rightIntAsString.Length - 4, 4);

            string d = rightIntAsString.Substring(0, rightIntAsString.Length - 4);

​

            int aInt = Convert.ToInt32(a);

            int cInt = Convert.ToInt32(c);

​

            int sum = aInt + cInt + reminder;

            reminder = sum / 10000;

​

            if (b.Length > 4 || d.Length > 4)

            {

                return GetBigSum(b, d, ref reminder) + (sum % 10000).ToString("0000");

            }

​

            int bInt = string.IsNullOrEmpty(b) ? 0 : Convert.ToInt32(b);

            int dInt = string.IsNullOrEmpty(d) ? 0 : Convert.ToInt32(d);

​

            int higherSum = bInt + dInt + reminder;

​

            reminder = higherSum / 10000;

​

            return (higherSum % 10000).ToString("0000") + (sum % 10000).ToString("0000");

        }

​

        static string GetBigProduct(string leftIntAsString, string rightIntAsString, ref int reminder)

        {

            if (leftIntAsString.Length <= 4 && rightIntAsString.Length <= 4)

            {

                int aInteger = Convert.ToInt32(leftIntAsString);

                int cInteger = Convert.ToInt32(rightIntAsString);

​

                int product = aInteger * cInteger + reminder;

                reminder = product / 10000;

​

                return (product % 10000).ToString("0000");

            }

​

            if (leftIntAsString.Length < 4 && rightIntAsString.Length < 4)

            {

                leftIntAsString = leftIntAsString.PadLeft(4, '0');

                rightIntAsString = rightIntAsString.PadLeft(4, '0');

            }

​

            if (leftIntAsString.Length < rightIntAsString.Length)

            {

                leftIntAsString = leftIntAsString.PadLeft(rightIntAsString.Length, '0');

            }

​

            if (rightIntAsString.Length < leftIntAsString.Length)

            {

                rightIntAsString = rightIntAsString.PadLeft(leftIntAsString.Length, '0');

            }

​

            string a = leftIntAsString.Substring(leftIntAsString.Length - 4, 4);

            string b = leftIntAsString.Substring(0, leftIntAsString.Length - 4);

​

            string c = rightIntAsString.Substring(rightIntAsString.Length - 4, 4);

            string d = rightIntAsString.Substring(0, rightIntAsString.Length - 4);

​

            int aInt = Convert.ToInt32(a);

            int cInt = Convert.ToInt32(c);

​

            int rightSum = GetRightPart(a, c) + reminder;

​

            reminder = rightSum / 10000;

            string rightPart = (rightSum % 10000).ToString("0000");

​

            string middlePart = GetMiddlePart(leftIntAsString, rightIntAsString, ref reminder);

            string reminderString = middlePart.Substring(0, middlePart.Length - 4);

​

            reminder += string.IsNullOrEmpty(reminderString) ? 0 : Convert.ToInt32(reminderString);

            middlePart = middlePart.Substring(middlePart.Length - 4, 4);

​

            string leftPart = GetLeftPart(b, d, ref reminder);

​

            return leftPart + middlePart + rightPart;

        }

}