#include <bits/stdc++.h>   using namespace std;   int main() {     long long t = 1;     while (t--) {       string s;       cin >> s;       sort(s.begin(), s.end());       long long n = s.size(), ans = 0;       long long l = 0, r = n - 1;       while (l <= r) {         long long m = l + (r - l) / 2;         if (s[m] == s[n - 1]) {           if (s[m - 1] != s[n - 1] || m == 0) {             ans = m;             break;           } else             r = m - 1;         } else {           l = m + 1;         }       }       cout << s.substr(ans) << endl;     }   }   