import java.util.Arrays;

public class Core {

	final int min;
	final int max;
	final int stringLength;

	private final int[] chars;

	public Core(char min, char max, int len) {
		this.min = min;
		this.max = max;
		this.stringLength = len;
		chars = new int[stringLength + 1];
		Arrays.fill(chars, 1, chars.length, min);
	}

	public void run() {
		while(chars[0] == 0) {
			print();
			increment();
		}
	}

	private void increment() {
		for(int i = chars.length - 1; i >= 0; i--) {
			if(chars[i] < max) {
				chars[i]++;
				return;
			}
			chars[i] = min;
		}
	}

	private void print() {
		for(int i = 1; i < chars.length; i++) {
			System.out.print((char) chars[i]);
		}
		System.out.println();
	}

	public static void main(String[] args) {
		new Core('a', 'z', 4).run();
	}
}