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;
using LINT = long long int;
using PII = pair<int, int>;
int m;
string s;
int ans[26];
set<int> covered;
int ccnt[26];
set<int> cpos[26];
bool iscovered(int l, int r) {
  if (!covered.size()) return false;
  auto lit = covered.lower_bound(l);
  if (lit == covered.end()) return false;
  return *lit <= r;
}
int findin(int c, int l, int r) {
  auto uit = cpos[c].upper_bound(r);
  if (uit == cpos[c].begin()) return -1;
  if (uit == cpos[c].end())
    if (*cpos[c].rbegin() >= l) return *cpos[c].rbegin();
  uit--;
  if (*uit >= l) return *uit;
  return -1;
}
int main() {
  cin >> m >> s;
  for (int i = 0; i < (s.size()); ++i) {
    cpos[s[i] - 'a'].insert(i);
    ccnt[s[i] - 'a']++;
  }
  for (int j = 0; j < (26); ++j) {
    for (int i = 0; i < (s.size() - m + 1); ++i) {
      if (iscovered(i, i + m - 1)) continue;
      int pos = findin(j, i, i + m - 1);
      if (pos != -1) {
        covered.insert(pos);
        ans[j]++;
      }
    }
  }
  int maxc = -1;
  for (int i = 0; i < (26); ++i)
    if (ans[i]) maxc = i;
  for (int i = 0; i < (maxc); ++i) ans[i] = ccnt[i];
  for (int i = 0; i < (26); ++i)
    while (ans[i]--) cout << char('a' + i);
  cout << endl;
  return 0;
}
