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 MAXN = 1e5 + 10;
char str[MAXN], ansstr[MAXN];
int n, num[MAXN], vis[MAXN];
struct Node {
  int l, r;
  int minval;
  Node(int l = 0, int r = 0, int minval = 0) : l(l), r(r), minval(minval){};
} node[MAXN * 4];
void build(int st, int ed, int k) {
  node[k].l = st;
  node[k].r = ed;
  if (st == ed) {
    node[k].minval = num[st];
    return;
  }
  int mid = (st + ed) >> 1;
  build(st, mid, (k << 1));
  build(mid + 1, ed, (k << 1 | 1));
  node[k].minval = min(node[(k << 1)].minval, node[(k << 1 | 1)].minval);
}
int query(int st, int ed, int k) {
  if (st == node[k].l && ed == node[k].r) {
    return node[k].minval;
  }
  if (node[(k << 1)].r >= ed) {
    return query(st, ed, (k << 1));
  } else if (node[(k << 1 | 1)].l <= st) {
    return query(st, ed, (k << 1 | 1));
  } else {
    return min(query(st, node[(k << 1)].r, (k << 1)),
               query(node[(k << 1 | 1)].l, ed, (k << 1 | 1)));
  }
}
int main() {
  while (~scanf("%d", &n)) {
    int val, pos, maxval = -1, minval = 0x3f3f3f3f;
    ;
    vector<int> ans;
    scanf("%s", str);
    int len = strlen(str);
    if (n > len) {
      for (int i = 0; i < len; i++) {
        minval = min(minval, (str[i] - 'a'));
      }
      ansstr[0] = (minval + 'a');
      ansstr[1] = '\0';
      printf("%s\n", ansstr);
      continue;
    }
    memset(vis, 0, sizeof(vis));
    for (int i = 0; i < len; i++) {
      num[i + 1] = str[i] - 'a';
    }
    build(1, len, 1);
    for (int i = 1; i <= len - n + 1; i++) {
      val = query(i, min(len, i + n - 1), 1);
      pos = 0;
      for (int j = i; j <= i + n - 1; j++) {
        if (num[j] == val) {
          pos = j;
        }
      }
      ans.push_back(pos);
      i = pos;
      vis[pos] = 1;
      maxval = max(maxval, num[pos]);
    }
    for (int i = 1; i <= len; i++) {
      if (num[i] < maxval && !vis[i]) {
        ans.push_back(i);
      }
    }
    for (int i = 0; i < ans.size(); i++) {
      ans[i] = num[ans[i]];
    }
    sort(ans.begin(), ans.end());
    for (int i = 0; i < ans.size(); i++) {
      ansstr[i] = (ans[i] + 'a');
    }
    ansstr[ans.size()] = '\0';
    printf("%s\n", ansstr);
  }
  return 0;
}
