#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <iomanip>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(long long i = 0;i < n;++i)
#define LONG_INF 100000000000000
int check(string a, string b) {
	if (a.length() < b.length()) {
		return 1;
	}
	else if (a.length() > b.length()) {
		return 0;
	}else{
		for (int i = 0;i < a.length();++i) {
			if (a[i] < b[i]) return 1;
			if (a[i] > b[i]) return 0;
		}
		return 0;
	}
}
int main() {
	string a[2], b[2], c[2];
	REP(i, 2) {
		cin >> a[i] >> b[i] >> c[i];
	}
	if (check(b[0],b[1])) {
		cout << a[1] << endl;
	}
	else if(b[0] == b[1]){
		cout << -1 << endl;
	}
	else cout << a[0] << endl;
	return 0;
}