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;
void Read(int &n) {
  int sign = 1;
  n = 0;
  char c;
  do {
    c = getchar();
  } while (!isdigit(c) && c != '-');
  if (c == '-') {
    c = getchar();
    sign = -1;
  }
  do {
    n = n * 10 + c - 48;
    c = getchar();
  } while (isdigit(c));
  n *= sign;
}
void Read(long long &n) {
  int sign = 1;
  n = 0;
  char c;
  do {
    c = getchar();
  } while (!isdigit(c) && c != '-');
  if (c == '-') {
    c = getchar();
    sign = -1;
  }
  do {
    n = n * 10ll + c - 48;
    c = getchar();
  } while (isdigit(c));
  n *= sign;
}
void Write(int n) {
  if (n == 0) {
    putchar('0');
    return;
  } else if (n < 0)
    putchar('-'), n = -n;
  char C[30];
  int d = 0;
  while (n) {
    C[++d] = (n % 10) + 48;
    n /= 10;
  }
  for (int i = d; i >= 1; --i) putchar(C[i]);
}
void Write(long long n) {
  if (n == 0) {
    putchar('0');
    return;
  } else if (n < 0)
    putchar('-'), n = -n;
  char C[30];
  int d = 0;
  while (n) {
    C[++d] = (n % 10ll) + 48;
    n /= 10ll;
  }
  for (int i = d; i >= 1; --i) putchar(C[i]);
}
const int maxn = 1e5 + 5;
char W[maxn];
int n, m;
int cnt[30];
int Get(int c) {
  int pre = 0, cur = 0, ret = 0;
  for (int i = 1; i <= n; ++i) {
    if (W[i] < 'a' + c) pre = i, cur = i;
    if (W[i] == 'a' + c) cur = i;
    if (i - pre == m) {
      if (cur > pre)
        pre = cur, ret++;
      else
        return -1;
    }
  }
  return ret;
}
int main() {
  scanf("%d", &m);
  scanf("%s", W + 1);
  n = strlen(W + 1);
  for (int i = 1; i <= n; ++i) cnt[W[i] - 'a']++;
  for (int i = 0; i <= 25; ++i) {
    int c = Get(i);
    if (c != -1) {
      for (int j = 0; j < i; ++j)
        for (int k = 1; k <= cnt[j]; ++k) putchar('a' + j);
      for (int k = 1; k <= c; ++k) putchar('a' + i);
      return 0;
    }
  }
  return 0;
}
