import java.util.*;

public class Main{
    public static int  pow(int a,int b){
        int res=1;
        while (b>0){
            if (b%2==1){
                res*=a;
            }
            a*=a;b>>=1;
        }
        return res;
    }
    public static int pow(int a,int b,int mod){
        int res=1;
        while (b>1){
            if (b%2==1){
                res=res*a%mod;
            }
            a=a*a%mod;b>>=1;
        }
        return res;
    }
    public static int abs(int a){
        if (a<0){
            return -a;
        }
        return a;
    }

    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        String a=sc.next();
        String b=sc.next();sc.next();
        String c=sc.next();
        String d=sc.next();sc.next();
        String ans=c;
        if (b.equals(d)){
            ans="-1";
        } else if (b.length()>d.length() || b.compareTo(d)>0){
            ans=a;
        }
        System.out.println(ans);
        sc.close();
    }
}