You are given a string s, consisting of lowercase English letters, and the integer m.

One should choose some symbols from the given string so that any contiguous subsegment of length m has at least one selected symbol. Note that here we choose positions of symbols, not the symbols themselves.

Then one uses the chosen symbols to form a new string. All symbols from the chosen position should be used, but we are allowed to rearrange them in any order.

Formally, we choose a subsequence of indices 1 ≤ i1 < i2 < ... < it ≤ |s|. The selected sequence must meet the following condition: for every j such that 1 ≤ j ≤ |s| - m + 1, there must be at least one selected index that belongs to the segment [j, j + m - 1], i.e. there should exist a k from 1 to t, such that j ≤ ik ≤ j + m - 1.

Then we take any permutation p of the selected indices and form a new string sip1sip2... sipt.

Find the lexicographically smallest string, that can be obtained using this procedure.

Input

The first line of the input contains a single integer m (1 ≤ m ≤ 100 000).

The second line contains the string s consisting of lowercase English letters. It is guaranteed that this string is non-empty and its length doesn't exceed 100 000. It is also guaranteed that the number m doesn't exceed the length of the string s.

Output

Print the single line containing the lexicographically smallest string, that can be obtained using the procedure described above.

Examples

Input

3
cbabc


Output

a


Input

2
abcab


Output

aab


Input

3
bcabcbaccba


Output

aaabb

Note

In the first sample, one can choose the subsequence {3} and form a string "a".

In the second sample, one can choose the subsequence {1, 2, 4} (symbols on this positions are 'a', 'b' and 'a') and rearrange the chosen symbols to form a string "aab".
#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
int m, n, sum[100005], sum2[100005], dq, num, f[100005];
;
string ans;
char s[100005];
int main() {
  scanf("%d", &m);
  scanf("%s", s + 1);
  n = strlen(s + 1);
  memset(sum, 0, sizeof(sum));
  ans = "";
  for (int z = 0; z < 26; ++z) {
    for (int i = 1; i <= n; ++i) sum2[i] = 0;
    sum2[0] = 0;
    for (int i = 1; i <= n; ++i) {
      if (s[i] == 'a' + z) {
        int l;
        l = i - m + 1;
        l = max(l, 1);
        sum2[l]++;
        sum2[i + 1]--;
      }
    }
    for (int i = 1; i <= n; ++i) {
      sum2[i] += sum2[i - 1];
    }
    for (int i = 1; i <= n; ++i) sum2[i] += sum[i];
    bool flag = true;
    for (int i = 1; i <= n - m + 1; ++i)
      if (sum2[i] == 0) flag = false;
    if (!flag) {
      for (int i = 1; i <= n; ++i)
        if (s[i] == 'a' + z) ans += s[i];
      for (int i = 1; i <= n; ++i) sum[i] = sum2[i];
      continue;
    }
    num = 0;
    for (int i = 1; i <= n; ++i)
      if (s[i] == 'a' + z) {
        ++num;
        f[num] = i;
      }
    f[0] = 0;
    dq = 0;
    ++num;
    f[num] = 1e9;
    for (int i = 1; i <= n - m + 1; ++i) {
      if (sum[i] != 0) continue;
      if (i <= f[dq] && f[dq] <= i + m - 1) continue;
      while (f[dq] <= i + m - 1) ++dq;
      dq--;
      ans += 'a' + z;
    }
    break;
  }
  cout << ans << endl;
  return 0;
}
