import java.io.*;
import java.util.*;
import java.math.*;

class Main201 {
	
	public static void out (Object out) {
		System.out.println(out);
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		String[] line1 = br.readLine().split(" ");
		String[] line2 = br.readLine().split(" ");
		
		if (line1[1].compareTo(line2[1]) > 0) {
			out(line1[0]);
		} else if (line1[1].compareTo(line2[1]) < 0) {
			out(line2[0]);
		} else {
			out(-1);
		}
	}
}