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