import java.util.Scanner;

public class No201 {

	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] spx1 = scanner.nextLine().split(" ");
		String[] spx2 = scanner.nextLine().split(" ");
		
		scanner.close();
		
		int len1 = spx1[1].length();
		int len2 = spx2[1].length();
		
		String ans = "";
		
		if(len1 > len2) {
			ans = spx1[0];
		}else if(len1 < len2) {
			ans = spx2[0];
		}else {
			
			int compare = spx1[1].compareTo(spx2[1]);
			
			if( compare> 0) {
				ans = spx1[0];
			}else if(compare < 0) {
				ans = spx2[0];
			}else {
				ans = "-1";
			}
		}
		
		System.out.println(ans);
		

	}

}