#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    string sa, pa, xa, sb, pb, xb;
    cin >> sa >> pa >> xa >> sb >> pb >> xb;

    if(pa == pb)
        cout << -1 << endl;
    else if(pa.size() < pb.size() || (pa.size() == pb.size() && pa < pb))
        cout << sb << endl;
    else
        cout << sa << endl;

    return 0;
}