#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  unordered_map<char, int> m;
  for (int i = 0; i < n; i++) {
    m[s[i]]++;
  }
  string ans = "";
  for (auto x : m) {
    for (int i = 0; i < x.second; i++) {
      ans += x.first;
    }
  }
  cout << ans;
}
