// This program reads in a string of N distinct letters in alphabetical order
// and prints all K-letter strings from it also in alphabetical order.

import java.util.*;

public class NchooseK {

	public static void main(String[] args) {

		// Read input data
		Scanner sc = new Scanner(System.in);
		int numOfLetters = sc.nextInt();
		String str = sc.next();

		generate(numOfLetters, str);
	}

	// Driver (auxiliary) method to call recursive method 
	public static void generate(int k, String str) {
		// Fill in the code

	}

}