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 n, m;
char s[1 << 20], ans[1 << 20];
int cnt[256], anss, dp[1 << 20];
int st[1 << 20];
void put(int x, int v) {
  for (int i = x; i <= n + m; i += i & (-i)) {
    st[i] = min(st[i], v);
  }
}
int get(int x) {
  int v = 19930309;
  for (int i = x; i >= 1; i -= i & (-i)) {
    v = min(v, st[i]);
  }
  return v;
}
void gao(int c) {
  for (int i = 0; i < n; ++i) {
    cnt[s[i]]++;
  }
  for (int i = 1; i <= n + m; i++) {
    st[i] = 19930309;
  }
  put(n + 1, 0);
  for (int i = 0; i < n; i++) {
    if (s[i] < c) {
      dp[i] = get(n - i + m);
    } else if (s[i] > c) {
      dp[i] = 19930309;
    } else {
      dp[i] = get(n - i + m) + 1;
    }
    put(n - i, dp[i]);
  }
  cnt[c] = get(m);
  for (int i = 'a'; i <= c; i++) {
    for (int j = 0; j < cnt[i]; j++) {
      ans[anss++] = i;
    }
  }
  puts(ans);
}
int main() {
  scanf("%d%s", &m, s);
  n = strlen(s);
  for (int i = 'a'; i <= 'z'; i++) {
    bool c = true;
    for (int j = 0, lst = -1; j < n; j++) {
      if (s[j] <= i) {
        lst = j;
      }
      if (j - lst >= m) {
        c = false;
        break;
      }
    }
    if (c) {
      gao(i);
      break;
    }
  }
}
