#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<int> count(26, 0);
  int n;
  string s;
  cin >> n >> s;
  for (auto c : s) {
    ++count[c - 'a'];
  }
  string result("");
  for (int i = 0; i < 26; ++i) {
    string tmp(count[i], static_cast<char>(i + 'a'));
    result += tmp;
  }
  cout << result << endl;
  return 0;
}
