#include <bits/stdc++.h>
using namespace std;
inline int read() {
  register int x = 0, o = 1;
  register char ch = getchar();
  while ((ch < '0' || ch > '9') && ch != '-') ch = getchar();
  if (ch == '-') o = -1, ch = getchar();
  while (ch >= '0' && ch <= '9')
    x = ((x << 3) + (x << 1)) + ch - '0', ch = getchar();
  return x * o;
}
int n;
char s[201000];
struct mona {
  int num;
  char ch;
} t[201000];
inline bool cmp(mona x, mona y) { return x.num > y.num; }
int main() {
  n = read(), scanf("%s", s + 1);
  for (register int i = 0; i < 26; ++i) t[i].ch = 'a' + i;
  for (register int i = 1; i <= n; ++i) t[s[i] - 'a'].num++;
  for (register int i = 0; i < 26; ++i)
    for (register int j = 1; j <= t[i].num; ++j) printf("%c", t[i].ch);
}
