#include <iostream>
#include <algorithm>
using namespace std;
#define FOR(i, a, b) for (int i=(a);i<(b);i++)
#define RFOR(i, a, b) for (int i=(b)-1;i>=(a);i--)
#define REP(i, n) for (int i=0;i<(n);i++)
#define RREP(i, n) for (int i=(n)-1;i>=0;i--)
#define INF 999999999
#define ll long long
#define pb(x) push_back(x) 

int main() {
  char n[500001];
  while(cin >> n) ;
  sort(n, n+500000);
  RREP(i, 500000) cout << n[i];
  cout << n[i] << endl;
  return 0;
}