import java.util.Random;

public class Testaa {

	public static void main(String[] args) {
		
		String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcedfghijklmnopqrstuvwxyz1234567890";
		Random random = new Random();
		StringBuffer bu = new StringBuffer();
		String a = "";
		for (int i = 0; i < 4; i++) {
			int number = random.nextInt(str.length());
			a = bu.append(str.charAt(number)).toString();
		}
		System.out.println(a);
	}

}