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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		FastScanner in = new FastScanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskD solver = new TaskD();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskD {
		public void solve(int testNumber, FastScanner in, PrintWriter out) {
			int m = in.nextInt();
			char[] s = in.next().toCharArray();
			int n = s.length;
			boolean[] taken = new boolean[n];
			for (int step = 0; step < 26; step++) {
				char ch = (char) (step + 'a');
				for (int i = 0; i < n; i++) {
					if (s[i] == ch) {
						taken[i] = true;
					}
				}
				boolean allCovered = true;
				int lastTaken = -1;
				for (int i = 0; i < n; i++) {
					if (taken[i]) {
						lastTaken = i;
					} else if (i - lastTaken >= m) {
						allCovered = false;
						break;
					}
				}
				if (!allCovered) {
					continue;
				}
				for (int i = 0; i < n; i++) {
					if (s[i] == ch) {
						taken[i] = false;
					}
				}
				lastTaken = -1;
				int lastCh = -1;
				for (int i = 0; i < n; i++) {
					if (s[i] == ch) {
						lastCh = i;
					}
					if (taken[i]) {
						lastTaken = i;
					} else if (i - lastTaken >= m) {
						taken[lastCh] = true;
						lastTaken = lastCh;
					}
				}
				break;
			}

			int[] a = new int[26];
			for (int i = 0; i < n; i++) {
				if (taken[i]) {
					++a[s[i] - 'a'];
				}
			}
			StringBuilder ans = new StringBuilder();
			for (int i = 0; i < a.length; i++) {
				for (int j = 0; j < a[i]; j++) {
					ans.append((char) (i + 'a'));
				}
			}
			out.println(ans);
		}

	}

	static class FastScanner {
		private BufferedReader in;
		private StringTokenizer st;

		public FastScanner(InputStream stream) {
			in = new BufferedReader(new InputStreamReader(stream));
		}

		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				try {
					String rl = in.readLine();
					if (rl == null) {
						return null;
					}
					st = new StringTokenizer(rl);
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

	}
}

