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 NX = 123456;
const int ALPHAX = 'z' + 2;
char a[NX];
int N;
int SIZE;
int nearest[ALPHAX][NX];
set<int> s[ALPHAX];
struct BinaryIndexedTree {
  int data[NX];
  BinaryIndexedTree() { memset(data, 0, sizeof(data)); }
  void up(int pos, int v) {
    for (int node = pos; node <= N; node += node & -node) {
      data[node] += v;
    }
  }
  int get(int pos) {
    int res = 0;
    for (int node = pos; node > 0; node -= node & -node) {
      res += data[node];
    }
    return res;
  }
  int get(int LL, int RR) { return get(RR) - get(LL - 1); }
} BIT;
int main() {
  scanf("%d %s", &SIZE, a + 1);
  N = strlen(a + 1);
  for (int i = 1; i <= N; i++) {
    for (char c = 'a'; c <= 'z'; c++) {
      if (a[i] == c)
        nearest[c][i] = i;
      else
        nearest[c][i] = nearest[c][i - 1];
    }
    s[a[i]].insert(i);
  }
  string res;
  for (char c = 'a'; c <= 'z'; c++) {
    int finished = true;
    for (int i = 1; i <= N - SIZE + 1; i++) {
      int where = nearest[c][i + SIZE - 1];
      if (BIT.get(i, i + SIZE - 1) == 0 && where >= i && s[c].count(where)) {
        s[c].erase(where);
        BIT.up(where, 1);
        res += c;
      } else if (BIT.get(i, i + SIZE - 1) == 0) {
        finished = false;
      }
    }
    if (finished) break;
    for (int where : s[c]) {
      BIT.up(where, 1);
      res += c;
    }
    s[c].clear();
  }
  cout << res;
}
