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 long mod = 1e9 + 7;
const long long maxn = 1e5 + 7;
const long long maxe = 1e6 + 7;
const long long INF = 1e9 + 7;
const double PI = acos(-1);
int dx[4] = {0, 0, 1, -1};
int dy[4] = {-1, 1, 0, 0};
inline void Max(int &a, int b) {
  if (b > a) a = b;
}
inline void Min(int &a, int b) {
  if (a == -1 || b < a) a = b;
}
int n, m;
string S;
int pos[30];
int seg[maxn * 4];
void build(int k, int l, int r) {
  if (l == r) {
    seg[k] = INF;
    return;
  }
  build(k << 1, l, (l + r) / 2);
  build(k << 1 | 1, (l + r) / 2 + 1, r);
  seg[k] = min(seg[(k << 1)], seg[(k << 1 | 1)]);
}
int query(int k, int l, int r, int a, int b) {
  if (a > r || b < l) return INF;
  if (l >= a && r <= b)
    return seg[k];
  else {
    return min(query(k << 1, l, (l + r) / 2, a, b),
               query(k << 1 | 1, (l + r) / 2 + 1, r, a, b));
  }
}
void change(int k, int l, int r, int a, int x) {
  if (a > r || a < l)
    return;
  else if (l == r) {
    seg[k] = min(seg[k], x);
    return;
  }
  change(k << 1, l, (l + r) / 2, a, x);
  change(k << 1 | 1, (l + r) / 2 + 1, r, a, x);
  seg[k] = min(seg[(k << 1)], seg[(k << 1 | 1)]);
}
int solve(char c) {
  build(1, 0, n);
  change(1, 0, n, 0, 0);
  for (int i = 1; i <= n; i++) {
    char t = S[i - 1];
    if (t > c) continue;
    int res = query(1, 0, n, i - m, i - 1);
    if (res == INF) return res;
    change(1, 0, n, i, res + ((t == c) ? 1 : 0));
  }
  int res = query(1, 0, n, n - m + 1, n);
  return res;
}
int main() {
  cin >> m >> S;
  n = S.length();
  for (int i = 0; i < S.length(); i++) {
    pos[S[i] - 'a']++;
  }
  string ans = "";
  for (int i = 0; i < 26; i++) {
    int t = solve(i + 'a');
    for (int j = 0; j < (t == INF ? pos[i] : t); j++) ans += ('a' + i);
    if (t != INF) break;
  }
  cout << ans << endl;
  return 0;
}
