#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <int n, class... T>
typename enable_if<(n >= sizeof...(T))>::type _ot(ostream &,
                                                  tuple<T...> const &) {}
template <int n, class... T>
typename enable_if<(n < sizeof...(T))>::type _ot(ostream &os,
                                                 tuple<T...> const &t) {
  os << (n == 0 ? "" : ", ") << get<n>(t);
  _ot<n + 1>(os, t);
}
template <class... T>
ostream &operator<<(ostream &o, tuple<T...> const &t) {
  o << "(";
  _ot<0>(o, t);
  o << ")";
  return o;
}
template <class T, class U>
ostream &operator<<(ostream &o, pair<T, U> const &p) {
  o << "(" << p.first << ", " << p.second << ")";
  return o;
}
template <class T>
ostream &operator<<(ostream &o, const stack<T> &a) {
  o << "{";
  for (auto tmp = a; tmp.size(); tmp.pop())
    o << (a.size() == tmp.size() ? "" : ", ") << tmp.top();
  o << "}";
  return o;
}
template <class T,
          class = typename iterator_traits<typename T::iterator>::value_type,
          class = typename enable_if<!is_same<T, string>::value>::type>
ostream &operator<<(ostream &o, const T &a) {
  for (auto ite = a.begin(); ite != a.end(); ++ite)
    o << (ite == a.begin() ? "" : " ") << *ite;
  return o;
}
int main() {
  std::ios::sync_with_stdio(false), std::cin.tie(0);
  int n;
  string s;
  cin >> n;
  cin >> s;
  map<char, int> mp;
  for (char c : s) mp[c]++;
  string ans;
  priority_queue<pair<int, char>> v;
  for (auto p : mp) {
    ans += string(p.second, p.first);
  }
  cout << ans << endl;
  return 0;
}
