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 long double pi = 3.1415926535897932384626433832795l;
const long long mod = 1000000007;
const int K = 330;
char S[100100];
int s[100100];
int dp[100100];
int cnt[50];
int main() {
  int n, m;
  cin >> m >> S;
  n = strlen(S);
  for (int i = 0; i < int(n); ++i) {
    s[i] = S[i] - 'a';
    cnt[s[i]]++;
  }
  s[n] = -1;
  for (int a = 0; a < int(26); ++a) {
    int j = -1, l = -1;
    for (int i = 0; i < int(n + 1); ++i) {
      if (s[i] > a) {
      } else if (j < i - m && l < i - m) {
        dp[i] = 1000000000;
      } else if (l >= i - m && l == -1) {
        dp[i] = s[i] == a;
      } else if (l >= i - m) {
        dp[i] = dp[l] + (s[i] == a);
      } else if (j == -1) {
        dp[i] = s[i] == a;
      } else {
        dp[i] = dp[j] + (s[i] == a);
      }
      if (s[i] < a) {
        l = i;
      }
      if (j < i - m) {
        if (s[i] == a) {
          j = i;
        }
      } else if (j == i - m) {
        for (int k = i - m + 1; k <= i; ++k) {
          if (s[k] == a) {
            j = k;
            break;
          }
        }
      }
    }
    if (dp[n] >= 1000000000) {
      for (int i = 0; i < int(cnt[a]); ++i) {
        cout << char('a' + a);
      }
      continue;
    }
    for (int i = 0; i < int(dp[n]); ++i) {
      cout << char('a' + a);
    }
    break;
  }
  return 0;
}
