Longest Block in String

using System;

namespace LongestBlockInString
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            int MaxSize = FindLongestSize(input);
            int index = FindIndex(input, MaxSize);
            Console.WriteLine(PrintString(input, index, MaxSize));
        }
        static string PrintString(string input, int index, int MaxSize)
        {
            string result = "";
            for (int i = index; i < index + MaxSize; i++)
            {
                result += input[i];
            }
            return result;
        }
        static int FindIndex(string input, int maxSize)
        {
            int index = 0;
            int size = 1;
            for (int i = 0; i < input.Length; i++)
            {
                if (input[i] == input[i + 1])
                {
                    size++;
                }
                else
                {
                    size = 1;
                }
                if (size == maxSize)
                {
                    index = i + 2 - size;
                    break;
                }
            }
            return index;
        }
        static int FindLongestSize(string input)
        {
            int longest = int.MinValue;
            int size = 1;
            for (int i = 0; i < input.Length - 1; i++)
            {
                if (input[i] == input[i + 1])
                {
                    size++;
                }
                else
                {
                    size = 1;
                }
                if (size > longest)
                {
                    longest = size;
                }
            }
            return longest;
        }
    }
}