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".
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ProblemD {

    public static Scanner sc;

    public static void main(String[] args) throws FileNotFoundException {
        sc = new Scanner(System.in);
//        sc = new Scanner(new File("input-d.txt"));
        new ProblemD().doTest();
    }

    private void doTest() {
        int m = Integer.parseInt(sc.nextLine());
        String s = sc.nextLine();

        for (char c = 'a'; c <= 'z'; c++) {
            String res = tryDo(s, m, c);
            if (res != null) {
                System.out.println(res);
                return;
            }
        }
    }

    private String tryDo(String s, int m, char maxChar) {
        int[] res = new int[1000];

        int lastTaken = -1;
        int lastPossible = -1;
        for (int i = 0; i < s.length(); i++) {
            char cur = s.charAt(i);
            if (cur < maxChar) {
                res[cur]++;
                lastTaken = i;
            } else if (cur == maxChar) {
                lastPossible = i;
            }

            if (i - lastTaken >= m) {
                if (lastPossible <= lastTaken) {
                    return null;
                } else {
                    lastTaken = lastPossible;
                    res[s.charAt(lastPossible)]++;
                }
            }
        }

        StringBuilder str = new StringBuilder();
        for (char c = 'a'; c <= 'z'; c++) {
            for (int i = 0; i < res[c]; i++) {
                str.append(c);
            }
        }

        return str.toString();
    }
}
