#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, count = 0;
  char b;
  cin >> n;
  int hash[26] = {0};
  string s;
  cin >> s;
  vector<char> v;
  for (int i = 0; i < n; i++) {
    v.push_back(s[i]);
    hash[s[i] - 'a']++;
  }
  sort(v.begin(), v.end());
  for (int i = 0; i < 26; i++) {
    if (hash[i] / 2 > 0 && hash[i] % 2 != 0 && count == 0) {
      count++;
      for (int k = 0; k < hash[i]; k++) {
        b = i + 'a';
        cout << b;
      }
    } else if (hash[i] > 0) {
      for (int k = 0; k < hash[i]; k++) {
        b = i + 'a';
        cout << b;
      }
    }
  }
  return 0;
}
