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 + 6;
int m;
int pos[maxn];
char s[maxn];
vector<int> ch[26];
int sumc[26];
int chose[maxn];
bool isOk(int len) {
  int index = 0;
  for (int i = 0; i < 26; ++i) {
    if (sumc[i] >= len) {
      index = i;
      break;
    }
  }
  int addc = index == 0 ? len : len - sumc[index - 1];
  int pre = -1;
  int maxp = -1;
  int n = strlen(s);
  for (int i = 0; i < n; ++i) {
    if (s[i] - 'a' < index) {
      pre = i;
      maxp = i;
    } else if (s[i] - 'a' == index) {
      maxp = i;
    }
    if (i - pre == m) {
      if (i - maxp >= m || addc <= 0) {
        return false;
      }
      pre = maxp;
      addc--;
    }
  }
  return true;
}
int main() {
  while (~scanf("%d", &m)) {
    for (int i = 0; i < 26; ++i) {
      ch[i].clear();
    }
    memset(sumc, 0, sizeof(sumc));
    scanf("%s", s);
    int n = strlen(s);
    for (int i = 0; i < n; ++i) {
      sumc[s[i] - 'a']++;
      ch[s[i] - 'a'].push_back(i);
    }
    for (int i = 1; i < 26; ++i) {
      sumc[i] += sumc[i - 1];
    }
    int posk = 0;
    for (int d = 0; d < 26; ++d) {
      for (int i = 0; i < ch[d].size(); ++i) {
        pos[posk++] = ch[d][i];
      }
    }
    int l = 1, r = n;
    while (l < r) {
      int mid = (l + r) >> 1;
      if (isOk(mid)) {
        r = mid;
      } else {
        l = mid + 1;
      }
    }
    int len = r;
    for (int i = 0; i < len; ++i) {
      printf("%c", s[pos[i]]);
    }
    puts("");
  }
  return 0;
}
