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>
#pragma comment(linker, "/STACK:268435456")
using namespace std;
template <typename T>
T sqr(const T &x) {
  return x * x;
}
template <typename T>
T my_abs(const T &x) {
  return x < 0 ? -x : x;
}
const int INF = (int)1e9;
const long long LINF = (long long)6e18;
const long long INF64 = LINF;
const long long INFLL = LINF;
const long double EPS = 1e-15;
const long double PI = 3.1415926535897932384626433832795;
const long double ME = 1e-5;
const long long MOD = (int)1e9 + 7;
const long long MOD2 = (int)1e9 + 21;
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
const int SQN = 320;
const int LOGN = 17;
const int N = (int)1e5 + 10;
int a[N];
int n, m;
int cnt[26];
bool check(int mv) {
  int lst = -1;
  int le = -1;
  memset(cnt, 0, sizeof(cnt));
  for (int i = 0; i < int(n); ++i) {
    if (lst + m < i) {
      if (le == -1) {
        return false;
      }
      lst = le;
      cnt[mv]++;
      if (lst + m < i) {
        return false;
      }
    }
    if (a[i] < mv) {
      cnt[a[i]]++;
      lst = i;
    } else if (a[i] == mv) {
      le = i;
    }
  }
  if (lst + m < n) {
    if (le == -1) {
      return false;
    }
    lst = le;
    cnt[mv]++;
    if (lst + m < n) {
      return false;
    }
  }
  if (lst == -1) {
    if (le == -1) {
      return false;
    }
    cnt[mv]++;
  }
  return true;
}
void solve() {
  string s;
  cin >> m >> s;
  for (int i = 0; i < int(int(s.size())); ++i) {
    a[i] = s[i] - 'a';
  }
  n = int(s.size());
  for (int mv = 0; mv < int(26); ++mv) {
    if (check(mv)) {
      string ans = "";
      for (int i = 0; i < int(26); ++i) {
        for (int k = 0; k < int(cnt[i]); ++k) {
          ans.push_back('a' + i);
        }
      }
      cout << ans << endl;
      return;
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  srand((unsigned int)time(NULL));
  cout << setprecision(15) << fixed;
  solve();
  return 0;
}
