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;
set<int> Set;
bool flag;
int n, m, Ans, Count, Pos[300010], Pre;
char str[300010], Deft;
inline int gcd(int x, int y) {
  if (!y) return x;
  return gcd(y, x % y);
}
inline void read(int &x) {
  char ch;
  int N = 1;
  while ((ch = getchar()) && (!((ch >= '0') && (ch <= '9'))) && (!(ch == '-')))
    ;
  if ((ch == '-')) {
    N = -1;
    while ((ch = getchar()) && (!((ch >= '0') && (ch <= '9'))))
      ;
  }
  x = ch - 48;
  while ((ch = getchar()) && (((ch >= '0') && (ch <= '9'))))
    x = x * 10 + ch - 48;
  x *= N;
}
inline void Insert(int x) {
  Pos[x] = x;
  Set.insert(x);
}
inline bool cmp(const int &x, const int &y) { return str[x] < str[y]; }
inline void Work(int x) {
  set<int>::iterator Item, Item_;
  Item = Item_ = Set.lower_bound(Pos[x]);
  if ((*Item) - (*(--Item_)) > m) flag = 0;
}
int main() {
  read(m);
  scanf("%s", str + 1);
  n = strlen(str + 1);
  for (int i = 1; i <= n; i++) Insert(i);
  Set.insert(0);
  Set.insert(n + 1);
  sort(Pos + 1, Pos + n + 1, cmp);
  flag = Ans = 1;
  for (int i = n; i >= 1; i--) {
    Set.erase(Pos[i]);
    Work(i);
    if (!flag) {
      Deft = str[Pos[i]];
      break;
    }
  }
  for (int i = 1; i <= n; i++) {
    if (Ans > m) Ans = i - Pre, Count++;
    if (str[i] < Deft) Ans = 0;
    Pre = (str[i] == Deft) ? (i) : (Pre);
    Ans++;
  }
  Count += (Ans > m);
  for (int i = 1; str[Pos[i]] != Deft; i++) printf("%c", str[Pos[i]]);
  for (int i = 1; i <= Count; i++) printf("%c", Deft);
  printf("\n");
}
