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;
inline long long in() {
  int32_t x;
  scanf("%d", &x);
  return x;
}
inline long long lin() {
  long long x;
  scanf("%lld", &x);
  return x;
}
inline string get() {
  char ch[2000010];
  scanf("%s", ch);
  return ch;
}
inline void read(long long *a, long long n) {
  for (long long i = 0; i < n; i++) a[i] = in();
}
template <class blank>
inline void out(blank x) {
  cout << x << "\n";
  exit(0);
}
const long long maxn = 1e5 + 10;
const long long maxm = 1e6 + 10;
const long long maxlg = 21;
const long long base = 29;
const long long mod = 1e9 + 7;
const long long INF = 1e18 + 10;
const long long SQ = 317 + 5;
long long mini[4 * maxn], n;
string s;
inline void build(long long p = 0, long long l = 0, long long r = n - 1) {
  if (l == r) {
    mini[p] = l;
    return;
  }
  long long mid = (l + r) >> 1;
  build(2 * p + 1, l, mid), build(2 * p + 2, mid + 1, r);
  if (s[mini[2 * p + 2]] <= s[mini[2 * p + 1]])
    mini[p] = mini[2 * p + 2];
  else
    mini[p] = mini[2 * p + 1];
}
inline long long get_mini(long long ql, long long qr, long long p = 0,
                          long long l = 0, long long r = n - 1) {
  if (l > qr || r < ql) return INF;
  if (l >= ql && r <= qr) return mini[p];
  long long mid = (l + r) >> 1;
  long long A = get_mini(ql, qr, 2 * p + 1, l, mid);
  long long B = get_mini(ql, qr, 2 * p + 2, mid + 1, r);
  if (A != INF && B != INF) {
    if (s[B] <= s[A]) return B;
    return A;
  } else if (A == INF)
    return B;
  else
    return A;
}
long long cnt[30];
long long cnt2[30];
int32_t main() {
  long long m = in();
  s = get();
  n = s.size();
  for (long long i = 0; i < n; i++) cnt2[s[i] - 'a']++;
  build();
  long long cur = 0;
  while (cur + m <= s.size()) {
    long long id;
    id = get_mini(cur, cur + m - 1);
    cnt[s[id] - 'a'] = min(cnt[s[id] - 'a'] + 1, cnt2[s[id] - 'a']);
    for (long long pt = s[id] - 'a' - 1; pt >= 0; pt--) {
      while (cnt[pt] < cnt2[pt]) cnt[pt]++;
    }
    cur = id + 1;
  }
  for (long long i = 0; i < 26; i++)
    while (cnt[i]--) cout << char(i + 'a');
  cout << "\n";
}
