#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 3;
int n, sl = 0;
string s;
char kq[N];
int d[30];
pair<int, int> ok[30];
vector<int> CL;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  cin >> s;
  for (int i = 0; i <= n - 1; ++i) d[s[i] - 'a']++;
  for (int i = 0; i <= 26; ++i)
    if (d[i] == 1) ok[++sl] = {i, -1};
  int cnt = 0;
  cerr << sl << " ";
  for (int i = 0; i <= 26; ++i) {
    if (d[i] == 2 && cnt < sl) ok[++cnt].second = i, d[i] = 0;
  }
  for (int i = 0; i <= 26; ++i)
    for (int j = 1; j <= d[i]; ++j)
      if (d[i] != 1) cout << char(i + 97);
  for (int i = 1; i <= sl; ++i) {
    if (ok[i].second != -1) cout << char(ok[i].second + 97);
    cout << char(ok[i].first + 97);
    if (ok[i].second != -1) cout << char(ok[i].second + 97);
  }
}
