#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <set>
#include <stack>
#include <queue>
#include <deque>
using namespace std;



#define TASK "negcycle"



string s;

char minb_p[200000], minb_s[200000];

int nom_p[200000], nom_s[200000], mind, maxk, n, idx;



int main() {



#ifdef _DEBUG

	freopen("debug.in", "r", stdin);

	freopen("debug.out", "w", stdout);

#else

	//freopen(TASK".in", "r", stdin);

	//freopen(TASK".out", "w", stdout);

	//freopen("input.txt", "r", stdin);

	//freopen("output.txt", "w", stdout);

#endif // _DEBUG



	ios_base::sync_with_stdio(0);

	cin.tie(0);

	cout.tie(0);

	cout.precision(6);





	cin >> s;

	n = s.size();

	minb_p[0] = s[0];

	nom_p[0] = 0;

	minb_s[n - 1] = s[n - 1];

	nom_s[n - 1] = n - 1;

	for (int i = 1; i<n; i++)

	{

		if (s[i] <= minb_p[i - 1])

		{

			minb_p[i] = s[i];

			nom_p[i] = i;

		}

		else

		{

			minb_p[i] = minb_p[i - 1];

			nom_p[i] = nom_p[i - 1];

		}

	}

	for (int i = n - 2; i >= 0; i--)

	{

		if (s[i] <= minb_s[i + 1])

		{

			minb_s[i] = s[i];

			nom_s[i] = i;

		}

		else

		{

			minb_s[i] = minb_s[i + 1];

			nom_s[i] = nom_s[i + 1];

		}

	}

	maxk = 0;

	mind = 1000000;

	for (int i = n - 1; i >= 0; i--)

	{

		if (s[i] - minb_p[i]==maxk && mind > i - nom_p[i] + 1 || s[i] - minb_p[i] > maxk)

		{

			idx = nom_p[i];

			mind = i - nom_p[i] + 1;

			maxk = s[i] - minb_p[i];

		}

		if (s[i] - minb_s[i] == maxk && mind > nom_s[i] - i + 1 || s[i] - minb_s[i] > maxk)

		{

			idx = i;

			mind = nom_s[i] - i + 1;

			maxk = s[i] - minb_s[i];

		}



	}

	cout << s.substr(idx, mind);



	return 0;

}