#include <iostream>
#include <string>

using namespace std;

string N;

char get_max(string N){
  char max = 0;
  for (int i=0;i<N.length();i++) {
    char target = N[i];
    max = (target > max) ? target : max;
  }
  return max;
}

int main(){
  cin >> N;
  char max = get_max(N);
  
  for (int i=0;i<N.length();i++) {
    if ((N[i]) != max) {
      for (int j=N.length()-1;j>=i+1;j--) {
        if (N[j] == max) {
          N[j] = N[i];
          N[i] = max;
        }
      }
    }
  }

  cout<<N<<endl;
}