#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s;
  cin >> n >> s;
  map<char, int> mp;
  for (int i = 0; i < n; i++) mp[s[i]]++;
  for (auto x : mp)
    while (x.second--) cout << x.first;
  cout << endl;
  ;
  return 0;
}
