import java.util.Random;

public class GenerateRandomString {
    private static final int MIN_LENGTH = 5;
    private static final int MAX_LENGTH = 25;
    private static final String[] PARTS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz".split("");

    public static void main(String[] args) {
	int length = 0; // random length string
	if (args.length > 0) {
	    try {
		length = Integer.parseInt(args[0]);
	    }
	    catch (Exception e) {
		System.out.println("String length is not a number");
	    }
	}

	System.out.println(generateRandomString(length));
    }

    private static String generateRandomString(int length) {
	Random generator = new Random();
	if (length == 0) {
	    length = MIN_LENGTH
		   + generator.nextInt(MAX_LENGTH - MIN_LENGTH);
	}

	String s = "";
	for (int i = 0; i < length; i++) {
	    s += PARTS[generator.nextInt(PARTS.length - 1) + 1];
	}
	return s;
    }
}