using System;

using System.Numerics;

public class Program

{

    private static int counter1 = 0;

    private static int counter2 = 0;

    private static int counter3 = 0;

    public static void Main()

    {

        BigInteger x =  BigInteger.Parse("1685287499328328297814655639278583667919355849391453456921116729");

        BigInteger y =  BigInteger.Parse("7114192848577754587969744626558571536728983167954552999895348492");

​

        var result = multiply(x, y);

        Console.WriteLine(counter1 );

        Console.WriteLine(counter2 );

        Console.WriteLine(counter3 );

        Console.WriteLine(result );

    }

    public static BigInteger multiply(BigInteger x,BigInteger y)

    {

        BigInteger result = 0;

​

        int size1 = GetSize(x);

        int size2 = GetSize(y);

​

        //find the max size of two integers

        int N = Math.Max(size1, size2);

​

        if (N < 2)

            return x * y;

​

        //Max length divided by two and rounded up

        N = (N / 2) + (N % 2);

​

        //The mulitplying factor for calculating a,b,c,d

        BigInteger m = BigInteger.Pow(10, N);

​

        BigInteger b = x % m;

        BigInteger a = x / m;

        BigInteger c = y / m;

        BigInteger d = y % m;

        Console.WriteLine("first number");

        Console.WriteLine(b );

        Console.WriteLine(a );

        Console.WriteLine("second number"); 

        Console.WriteLine(c );

        Console.WriteLine(d );

​

        BigInteger z0 = multiply(a, c);

        BigInteger z1 = multiply(b, d);

        BigInteger z2 = multiply(a + b, c + d);

        BigInteger ad_bc = (z2 - z1 - z0);

        Console.WriteLine("Sum ad + bc = " + ad_bc );   

        if(ad_bc == 105)

        {

            counter1++;

        }

        if(ad_bc == 72)

        {

            counter2++;

        }

        if(ad_bc == 12)

        {

            counter3++;

        }

        var pow = BigInteger.Pow( 10 ,N * 2);

        result =  ( pow * z0) + z1 + (ad_bc * m);

        return result;

    }

    public static int GetSize(BigInteger num)

    {

        int len = 0;

        while (num != 0)

        {

            len++;

            num /= 10;

        }

        return len;

    }

}