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 sz = 1e5 + 9;
int m, n, mn;
string second, os;
int segtree[4 * sz], pos[4 * sz];
int a[sz];
int more[30];
int can[30];
int have[30];
void build(int node, int l, int r) {
  if (l == r) {
    segtree[node] = a[l];
    pos[node] = l;
    return;
  }
  int mid = (l + r) >> 1;
  int son1 = node << 1;
  int son2 = son1 + 1;
  build(son1, l, mid);
  build(son2, mid + 1, r);
  if (segtree[son2] <= segtree[son1]) {
    segtree[node] = segtree[son2];
    pos[node] = pos[son2];
  } else {
    segtree[node] = segtree[son1];
    pos[node] = pos[son1];
  }
}
pair<int, int> query(int node, int l, int r, int ql, int qr) {
  if (l > qr || r < ql) return make_pair(100, sz + 1);
  if (l >= ql && r <= qr) return make_pair(segtree[node], pos[node]);
  int mid = (l + r) >> 1;
  int son1 = node << 1;
  int son2 = son1 + 1;
  pair<int, int> q1 = query(son1, l, mid, ql, qr);
  pair<int, int> q2 = query(son2, mid + 1, r, ql, qr);
  if (q2.first <= q1.first) return q2;
  return q1;
}
int main() {
  cin >> m >> second;
  os = second;
  n = second.size();
  for (int i = 0; i < n; ++i) {
    a[i] = second[i] - 'a';
  }
  build(1, 0, n - 1);
  second = "";
  int st = 0, en = 0;
  bool ok = 0;
  int lst;
  while (en < n) {
    en = st + m - 1;
    auto ret = query(1, 0, n - 1, st, en);
    second += ('a' + ret.first);
    have[ret.first]++;
    st = ret.second + 1;
    en = st + m - 1;
  }
  if (st < n) {
    auto ret = query(1, 0, n - 1, st, n - 1);
    for (int i = st; i < n; ++i) {
    }
  }
  sort(second.begin(), second.end());
  lst = second.back() - 'a';
  int cntlst = 0;
  for (auto u : second) {
    cntlst += (u - 'a' == lst);
  }
  second = "";
  for (int i = 0; i < n; ++i) {
    if (a[i] < lst) second.push_back('a' + a[i]);
  }
  while (cntlst--) second.push_back('a' + lst);
  sort(second.begin(), second.end());
  cout << second;
  return 0;
}
