#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<algorithm>
#include<vector>
#include<math.h>
#include<iomanip>
#include<stack>
#include<queue>
#include<set>
#include<map>

using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int , int>;

//const ll mod = 1000000007;
const ll mod = 998244353;
const ld pi = 3.14159265358979;

int f(string s , string t){
	if(s == t)return 0;
	if(s.size() > t.size())return 1;
    else if(s.size() < t.size())return 2;
    for(int i = 0; i < s.size(); i++){
    	int x = s[i] - '0';
    	int y = t[i] - '0';
    	//cout << x << " : " << y << endl;
    	if(x > y)return 1;
    	else if(x < y)return 2;
    }
    return 0;
}

int main() {
	//ios::sync_with_stdio(false);
	//cin.tie(0);
	//cout << fixed << setprecision(15);
	string s1 , s2 , s3;
	string t1 , t2 , t3;
	cin >> s1 >> s2 >> s3;
	cin >> t1 >> t2 >> t3;
	int x = f(s2 , t2);
	if(x == 0)cout << -1 << endl;
	else if(x == 1)cout << s1 << endl;
	else if(x == 2)cout << t1 << endl;
	return 0;
}