/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
    public static void main (String[] args) throws java.lang.Exception
    {
        // your code goes here
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] lines = br.readLine().split(" ");
        String aname  = lines[0];
        String apoint = lines[1];

        lines = br.readLine().split(" ");
        String bname  = lines[0];
        String bpoint = lines[1];
        
        if(apoint.equals(bpoint)){
            System.out.println(-1);
        }else{
            System.out.println(compare(apoint,bpoint)<0?bname:aname);
        }
    }
    
    public static int compare(String a,String b){
        if(a.length() != b.length()){
            return a.length() - b.length();
        }else{
            return a.compareTo(b);
        }
    }

}