#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int n;
  cin >> n;
  string s;
  cin >> s;
  string res(n, '$');
  map<char, int> cnt;
  for (auto t : s) {
    cnt[t]++;
  }
  int l = 0;
  for (auto [c, num] : cnt) {
    for (int i = 0; i < num; i++) {
      res[l] = c;
      l++;
    }
  }
  cout << res << '\n';
}
