#pragma GCC optimize("Ofast,no-stack-protector,fast-math",3)
#include <bits/stdc++.h>
#define ALL(x) begin(x), end(x)
#define All(x, l, r) &x[l], &x[r + 1]
using namespace std;
void file(){
  freopen("1.in", "r", stdin);
  freopen("1.out", "w", stdout);
}
using ll = long long;
int main(){
  // file();
  ios::sync_with_stdio(0), cin.tie(0);
  string s; cin >> s;
  map<string, int> mp;
  for(int i = 0; i < s.size(); i++) mp[s.substr(i, 1)]++;
  while(mp.size() > 1){
    auto k1 = *begin(mp);
    auto k2 = *--end(mp);
    string s1 = k1.first, s2 = k2.first;
    int c1 = k1.second, c2 = k2.second;
    mp.erase(s1); mp.erase(s2);
    int d = c2 / c1, r = c2 % c1;
    while(d--) s1 = s1 + s2;
    mp[s1] = c1 - r;
    if(r) mp[s1 + s2] = r;
  }
  auto [t, c] = *begin(mp);
  while(c--) cout << t;
  return 0;
}