#include <bits/stdc++.h>
using namespace std;
const long long maxn = 1e3 + 10;
const long long mod = 1e9 + 7;
const double pi = acos(-1.0);
const double eps = 1e-8;
struct node {
  long long x, y;
};
node a[maxn];
bool cmp(node p, node q) {
  if (p.x == q.x) {
    return p.y < q.y;
  }
  return p.x > q.x;
}
long long ok(string str) {
  long long len = str.length();
  for (long long i = 0, j = len - 1; i < len / 2; i++, j--) {
    if (len % 2 == 1 && i == len / 2) {
      continue;
    }
    if (str[i] != str[j]) {
      return 0;
    }
  }
  return 1;
}
long long f(string str) {
  long long cnt = 0, n = str.length();
  for (long long i = 0; i < n; i++) {
    for (long long j = i; j < n; j++) {
      string tmp = "";
      for (long long k = i; k <= j; k++) {
        tmp = tmp + str[k];
      }
      if (ok(tmp)) {
        cnt++;
      }
    }
  }
  return cnt;
}
int main() {
  long long n;
  string s;
  while (cin >> n >> s) {
    for (long long i = 0; i < 26; i++) {
      a[i].x = 0, a[i].y = i;
    }
    for (long long i = 0; i < n; i++) {
      long long t = s[i] - 'a';
      a[t].x++;
    }
    sort(a, a + 26, cmp);
    string str = "";
    for (long long i = 0; i < 26; i++) {
      while (a[i].x) {
        char c = 'a' + a[i].y;
        str = str + c;
        a[i].x--;
      }
    }
    cout << str << endl;
  }
  return 0;
}
