#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n, a[N];
char s[N];
int main() {
  scanf("%d%s", &n, s);
  for (int i = 0; i < n; ++i) ++a[(int)s[i]];
  for (int i = 0; i < 500; ++i)
    for (int j = 1; j <= a[i]; ++j) putchar(i);
  puts("");
  return 0;
}
