#include <bits/stdc++.h>
using namespace std;
inline void boost() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
}
vector<pair<char, int> > x;
int main() {
  boost();
  int n;
  cin >> n;
  string a;
  cin >> a;
  sort(a.begin(), a.end());
  int k = 1;
  for (int i = 0; i < a.size() - 1; i++) {
    if (a[i] == a[i + 1]) {
      k++;
    } else {
      x.push_back(make_pair(a[i], k));
      k = 1;
    }
  }
  x.push_back(make_pair(a[a.size() - 1], k));
  for (int i = 0; i < x.size(); i++) {
    for (int j = 1; j <= x[i].second; j++) {
      cout << x[i].first;
    }
  }
  exit(0);
}
