using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Find Most Popular Char");

        var str = "Ya ebal tvoy telky";

        Console.WriteLine("In: " + str);

        var result = FindMostPopularChar(str);

        Console.WriteLine("Result = " + result);

    }

       public static char FindMostPopularChar(string str)

        {

            char[] charsFromStr = str.ToCharArray();

            int[] charsCountArray = new int[str.Length];

            char[] uniqueCharsArray = new char[str.Length];

​

            int lastIndex = 0;

            bool found = false;

​

            for (int i = 0; i < charsFromStr.Length; i++)

            {

                for (int j = 0; j < uniqueCharsArray.Length; j++)

                {

                    if (uniqueCharsArray[j] == charsFromStr[i])

                    {

                        charsCountArray[j]++;

                        found = true;

                        break;

                    }

                }

                if (!found)

                {

                    uniqueCharsArray[lastIndex] = Char.ToLower(charsFromStr[i]);

                    charsCountArray[lastIndex] = 1;

                    lastIndex++;

                }

                found = false;

            }

​

            int max = 0;

            int popularIndex = 0;

            for (int i = 0; i < charsCountArray.Length; i++)

            {

                if (max < charsCountArray[i])

                {

                    max = charsCountArray[i];

                    popularIndex = i;

                }

            }

​

            char popularChar = uniqueCharsArray[popularIndex];

            return popularChar;

        }

}