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;
template <class T>
inline void umax(T &a, T b) {
  if (a < b) a = b;
}
template <class T>
inline void umin(T &a, T b) {
  if (a > b) a = b;
}
template <class T>
inline T abs(T a) {
  return a > 0 ? a : -a;
}
const int inf = 1e9 + 143;
const long long longinf = 1e18 + 143;
inline int read() {
  int x;
  scanf(" %d", &x);
  return x;
}
const int N = 1e5 + 100;
int n, m, to;
char s[N];
int f[N];
int cnt[26];
int calc(int at) {
  for (int i = 1; i <= n; i++) {
    f[i] = 0;
  }
  for (int i = 1; i <= n; i++) {
    if (s[i] - 'a' < at) {
      f[max(1, i - m + 1)] += 1;
      f[i + 1] -= 1;
    }
  }
  for (int i = 1; i <= n; i++) {
    f[i] += f[i - 1];
  }
  vector<int> st;
  int ptr = 1;
  int res = 0;
  for (int i = 1; i <= to; i++) {
    if (!f[i]) {
      while (ptr - m + 1 <= i) {
        if (s[ptr] - 'a' == at) {
          st.push_back(ptr);
        }
        ptr++;
      }
      if (st.size() == 0) {
        return -1;
      }
      int take = st.back();
      if (take < i) {
        return -1;
      }
      st.pop_back();
      res += 1;
      i = take;
    }
  }
  return res;
}
int main() {
  m = read();
  scanf(" %s", s + 1);
  n = strlen(s + 1);
  to = n - m + 1;
  for (int i = 1; i <= n; i++) {
    cnt[s[i] - 'a'] += 1;
  }
  for (int c = 0; c < 26; c++) {
    int best = calc(c);
    if (best != -1) {
      for (int i = 0; i < c; i++) {
        for (int k = 0; k < cnt[i]; k++) {
          printf("%c", i + 'a');
        }
      }
      for (int k = 0; k < best; k++) {
        printf("%c", c + 'a');
      }
      return 0;
    }
  }
  assert(0);
  return 0;
}
