#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cstring>

typedef long long ll;
using namespace std;

#define mod 1000000007
#define INF 1000000000 //(int)1e9
#define LLINF 2000000000000000000 //(ll)2e18
#define PI  3.1415926536

#define SIZE 100000

int main(){
    string a,b,pa,pb,xa,xb;
    
    cin >> a >> pa >> xa >> b >> pb >> xb;
    
    int d = a.size() - b.size();
    
    while(d==0){
        if(d<0){
            a = "0" + a;
            d++;
        }else{
            b = "0" + b;
            d--;
        }
    }
    
    if(pa < pb){
        cout << b;
    }else if(pa > pb){
        cout << a;
    }else{
        cout << -1;
    }
    
    cout << endl;
    
    
    return 0;
}