#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    string a,b,c,d,x,y;
    cin >> a >> x >> c >> b >> y >> d;

    if(x == y){
        cout << - 1<< endl;
        return 0;
    }

    int flag = 0;

    if(x.size() > y.size())flag = 1;

    if(x.size() == y.size()){
        rep(i,x.size()){
            if(x[i] > y[i])flag = 1;
            if(x[i] < y[i])break;
        }
    }

    if(flag) cout << a << endl;
    else cout << b << endl;
    return 0;
}