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.*;

public class CF724D {
	static boolean check(char[] cc, int m, int a, int b) {
		int n = cc.length;
		boolean[] bb = new boolean[n];	// bb[j]: m-block ending at j covered?
		for (int i = 0, j = m - 1; i < n; i++) {
			int c = cc[i] - 'a';
			if (c < a) {
				if (j < i)
					j = i;
				while (j < n && j < i + m) {
					bb[j] = true;
					j++;
				}
			}
		}
		for (int h = 0, j = m - 1; j < n; j++) {
			if (!bb[j] && b > 0)
				for (int i = j; i >= h; i--) {
					int c = cc[i] - 'a';
					if (c == a) {
						for (int k = j; k < n && k < i + m; k++)
							bb[k] = true;
						h = i + 1;
						b--;
						break;
					}
				}
			if (!bb[j])
				return false;
		}
		return true;
	}
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int m = Integer.parseInt(br.readLine());
		char[] cc = br.readLine().toCharArray();
		int n = cc.length;
		int[] kk = new int[26];
		for (int i = 0; i < n; i++) {
			int c = cc[i] - 'a';
			kk[c]++;
		}
		int lower = 0, upper = 26 * n;
		while (upper - lower > 1) {
			int x = (lower + upper) / 2;
			int a = x / n;
			int b = x % n;
			if (check(cc, m, a, b))
				upper = x;
			else
				lower = x;
		}
		int a = upper / n;
		int b = upper % n;
		StringBuilder sb = new StringBuilder();
		for (int c = 0; c < a; c++)
			for (int i = 0; i < kk[c]; i++)
				sb.append((char) ('a' + c));
		for (int i = 0; i < b; i++)
				sb.append((char) ('a' + a));
		System.out.println(sb);
	}
}
