#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  string alpha = "abcdefghijklmnopqrstuvwxyz";
  int a[26] = {0};
  for (int i = 0; i < n; i++) {
    a[s[i] - 'a']++;
  }
  for (int i = 0; i < 26; i++) {
    if (a[i] != 0) {
      string add(a[i], alpha[i]);
      cout << add;
    }
  }
  cout << endl;
  return 0;
}
