using System;
using System.Collections.Generic;
using System.Linq;

namespace _03.LongestBlock
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();

            string maxChar = new string(input
                .Select((x, index) => input.Substring(index)
                .TakeWhile(y => y == x))
                .OrderByDescending(x => x.Count())
                .First().ToArray());

            Console.WriteLine(maxChar);

        }
    }
}