using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string s1 = "HeloooWooLLLrLLd";

        //char[] s1 = str.ToCharArray();

        Dictionary<char,int> charCount = new Dictionary<char,int>();

        foreach(char i in s1){

        char c = char.ToLower(i);

        if(charCount.ContainsKey(c))

           {

               charCount[c]++;

           }

         else

         {

            charCount[c] = 1;

         }

        }

        int max = charCount.Values.Max();

        char findkey = charCount.FirstOrDefault(x => x.Value == max).Key;

        Console.WriteLine(findkey);

    }

}