#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <sstream>
#include <functional>
#include <map>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <list>
#include <numeric>
using namespace std;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = 1<<25;
typedef pair<int,int> P;
typedef long long ll;
typedef unsigned long long ull;

int comp(string &a, string &b){
	int n = a.size(), m = b.size();
	if(n!=m) return n-m;
	for(int i = 0; i < n; i++){
		if(a[i]==b[i]) continue;
		return a[i]-b[i];
	}
	return 0;
}

int main(){
	string a[2], b[2], c[2];
	for(int i = 0; i < 2; i++) cin>>a[i]>>b[i]>>c[i];
	if(b[0]==b[1]) cout<<-1<<endl;
	else cout<<(comp(b[0], b[1])>0?a[0]:a[1])<<endl;
	
	return 0;
}