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;
long long inf = 1e18, mod = 1e9 + 7;
double pi = 3.14;
long long gcd(long long a, long long b) {
  while (a > 0) {
    if (a > b) {
      swap(a, b);
    }
    b %= a;
  }
  return b;
}
long long nok(long long a, long long b) { return b; }
long long min3(long long a, long long b, long long c) {
  a = min(a, b);
  a = min(a, c);
  return a;
}
int main() {
  long long m;
  string s;
  cin >> m >> s;
  long long last = -1;
  for (char i = 'a'; i <= 'z'; i++) {
    bool can = 1;
    long long last = -1;
    for (int j = 0; j < s.length(); j++) {
      if (s[j] <= i) {
        last = j;
      }
      if (j - m >= last) {
        can = 0;
      }
    }
    if (can) {
      long long last = -1, lasti = -1;
      for (int j = 0; j < s.length(); j++) {
        if (s[j] < i) {
          last = j;
        } else if (s[j] == i) {
          lasti = j;
        }
        if (j - m >= last) {
          cout << i;
          last = lasti;
        }
      }
      return 0;
    } else if (!(can)) {
      for (int j = 0; j < s.length(); j++) {
        if (s[j] == i) {
          cout << i;
        }
      }
    }
  }
  return 0;
}
