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.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Deque;

public class SubsegmentMin {

	public void getMin(char[] input, int sl) {
		char max = 0;
		int maxCnt = 0;
		int prevMinIndex = 0;
		Deque<Integer> deque = new ArrayDeque<>();
		for (int i = 0; i <= input.length - 1; ++i) {
			while (true) {
				if (deque.isEmpty()) {
					deque.add(i);
					break;
				} else if (input[deque.peekLast()] > input[i]) {
					deque.pollLast();
				} else if (input[deque.peekLast()] < input[i]) {
					deque.add(i);
					break;
				} else {
					if (i + 1 <= sl) {
						deque.pollLast();
					} else {
						if (deque.peek() == deque.peekLast()) {
							deque.add(i);
							break;
						} else {
							deque.pollLast();
						}
					}
				}
			}
			if (i + 1 >= sl) {
				// System.out.println(input[deque.peek()]);
				if (deque.peek() + 1 < ((i + 1) - sl) + 1) {
					deque.poll();
				}
				if (max == 0) {
					max = input[deque.peek()];
					maxCnt = 1;
					prevMinIndex = deque.peek();
				} else if (input[deque.peek()] > max) {
					max = input[deque.peek()];
					maxCnt = 1;
					prevMinIndex = deque.peek();
				} else if (input[deque.peek()] == max) {
					if (deque.peek() != prevMinIndex) {
						++maxCnt;
						prevMinIndex = deque.peek();
					}
				}
				/*
				 * if (deque.peek() + 1 <= ((i + 1) - sl) + 1) { deque.poll(); }
				 */
			}
		}
		StringBuilder builder = new StringBuilder();
		int tempCnt = maxCnt;
		for (int i = 0; i <= input.length - 1; ++i) {
			if (input[i] < max) {
				builder.append(input[i]);
			} else if (input[i] == max) {
				if (tempCnt != 0) {
					builder.append(input[i]);
					--tempCnt;
				}
			}
		}
		char[] temp = builder.toString().toCharArray();
		Arrays.sort(temp);
		System.out.println(new String(temp));
	}

	public static void main(String[] args) {
		// invokeCustom();
		invokeActual();
	}

	private static void invokeActual() {
		try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
			int size = Integer.parseInt(reader.readLine());
			char[] input = reader.readLine().toCharArray();
			SubsegmentMin min = new SubsegmentMin();
			min.getMin(input, size);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	private static void invokeCustom() {
		java.util.Random random = new java.util.Random();
		char[] input = new char[35];
		for (int i = 0; i <= input.length - 1; ++i) {
			input[i] = (char) (97 + random.nextInt(26));
		}
	}

}
