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 N = 100005;
vector<int> Vec[26];
char s[N];
int fa[N], n, m, L[N], R[N], ok[N];
int getfa(int x) { return fa[x] == x ? x : fa[x] = getfa(fa[x]); }
void Modify(int L, int R) {
  L = getfa(L);
  while (L <= R) {
    fa[L] = L + 1;
    L = getfa(L);
  }
  return;
}
int main() {
  scanf("%d", &m);
  scanf("%s", s + 1);
  n = strlen(s + 1);
  for (int i = 1; i <= n; i++)
    L[i] = max(1, i - m + 1), R[i] = min(n, i + m - 1);
  for (int i = 1; i <= n; i++) Vec[s[i] - 97].push_back(i);
  for (int i = 1; i <= n + 1; i++) fa[i] = i;
  for (int i = 0; i < 26; i++) {
    int size = Vec[i].size();
    for (int j = 0; j < size; j++) {
      int Lest = getfa(1);
      if (j < size - 1 && L[Vec[i][j + 1]] <= Lest) continue;
      Modify(L[Vec[i][j]], Vec[i][j]);
      if (!ok[Vec[i][j]]) putchar(i + 97), ok[Vec[i][j]] = 1;
      if (getfa(1) > n - m + 1) return 0;
    }
    for (int j = 0; j < size; j++) {
      int Lest = getfa(1);
      Modify(L[Vec[i][j]], Vec[i][j]);
      if (!ok[Vec[i][j]]) putchar(i + 97), ok[Vec[i][j]] = 1;
      if (getfa(1) > n - m + 1) return 0;
    }
  }
  return 0;
}
