/* cs */

/* 
 * Problem  : 	SUBSTR
 * Contest  : 	UOI-2006 (Dnepropetrovsk)
 * Type     : 	Solution
 * Date     : 	March 25, 2006
 * Author   : 	Shamil Yagiyayev
 * Language :	C#
 * Compiler :	.NET 1.1
 * Algorithm:	Simple Solution
 */

using System;
using System.IO;
using System.Text;

class Substr
{
	static readonly string FILE_IN = "substr.dat";
	static readonly string FILE_OUT = "substr.sol";

	static string buffer = "";
	static int index = 0;

	static string best = "";
	static StreamReader sr = new StreamReader(FILE_IN);
	static readonly int MAX_SUBSTR = 26 + 1;

	static char[] currStr = new char[MAX_SUBSTR];
	static int fillNext = 0;

	static char GetChar()
	{
		while (buffer!=null && index == buffer.Length)
		{
			buffer = sr.ReadLine();
			index = 0;
		}

		if (buffer == null) return '-'; // means EOF

		return buffer[index++];
	}

	static void AddChar(char c)
	{
		currStr[fillNext] = c;
		fillNext = (fillNext + 1) % MAX_SUBSTR;
	}

	static string GetCurrentWord(int l)
	{
		int wordStart = (MAX_SUBSTR + fillNext - l) % MAX_SUBSTR;
		StringBuilder sb = new StringBuilder();
		for (int i=wordStart; i!=fillNext; i = (i+1) % MAX_SUBSTR) sb.Append(currStr[i]);
		return sb.ToString();
	}

	static char GetBackChar(int n)
	{
		return currStr[ (fillNext+MAX_SUBSTR - n) % MAX_SUBSTR];
	}

	static void Process()
	{
		int curr = 0;
		int wordLeng = 0;
		int currWordLeng = 0;
		char c = GetChar();
		while (c != '-')
		{
			AddChar(c);
			curr++;

			wordLeng = 1;
			while (wordLeng<=currWordLeng && c != GetBackChar(wordLeng+1)) wordLeng++;
			
			currWordLeng = wordLeng;
			
			if (wordLeng > best.Length) best = GetCurrentWord(wordLeng);
			
			c = GetChar();
		}
	}


	static void WriteSolution()
	{
		StreamWriter sw = File.CreateText(FILE_OUT);
		sw.WriteLine(best);
		sw.Close();
	}

	static void Main()
	{
		Process();
		WriteSolution();
	}
}