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;
int m, tot, l, r, mx, num, len, indx;
char s[100003], ch[27];
int cnt[255], pos[100003], all;
bool used[255];
void solve() {
  mx = 0;
  while (mx < tot) {
    r = 0;
    memset(used, false, sizeof(used));
    for (int i = 0; i <= mx; ++i) {
      used[ch[i]] = true;
    }
    num = 0;
    while (r < m) {
      if (used[s[r++]]) {
        ++num;
      }
    }
    if (num <= 0) {
      ++mx;
      continue;
    }
    while (r < len) {
      if (used[s[r]]) {
        ++num;
      }
      if (used[s[r - m]]) {
        --num;
      }
      if (num <= 0) {
        break;
      }
      ++r;
    }
    if (r == len) {
      return;
    }
    ++mx;
  }
}
int main() {
  while (2 == scanf("%d%s", &m, s)) {
    len = strlen(s);
    memset(cnt, 0, sizeof(cnt));
    tot = 0;
    for (int i = 0; i < len; ++i) {
      if (cnt[s[i]] == 0) {
        ch[tot++] = s[i];
      }
      ++cnt[s[i]];
    }
    sort(ch, ch + tot);
    solve();
    r = num = 0;
    cnt[ch[mx]] = 0;
    memset(used, false, sizeof(used));
    for (int i = 0; i < len; ++i) {
      if (s[i] == ch[mx]) {
        pos[all++] = i;
      }
    }
    for (int i = 0; i < mx; ++i) {
      used[ch[i]] = true;
    }
    while (r < m) {
      if (used[s[r++]]) {
        ++num;
      }
    }
    indx = -1;
    if (num <= 0) {
      indx = upper_bound(pos, pos + all, m - 1) - pos - 1;
      ++cnt[ch[mx]];
      ++num;
    }
    while (r < len) {
      if (used[s[r]]) {
        ++num;
      }
      if (used[s[r - m]]) {
        --num;
      }
      if (indx != -1 && pos[indx] <= r - m) {
        --num;
        indx = -1;
      }
      if (num <= 0) {
        indx = upper_bound(pos, pos + all, r) - pos - 1;
        ++cnt[ch[mx]];
        ++num;
      }
      ++r;
    }
    for (int i = 0; i <= mx; ++i) {
      while (--cnt[ch[i]] >= 0) {
        putchar(ch[i]);
      }
    }
    puts("");
  }
  return 0;
}
