#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#define p(s) cout<<(s)<<endl
#define REP(i,n,N) for(int i=n;i<N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=n;i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define F first
#define S second
typedef long long ll;
using namespace std;
const int mod = 1e9+7;

string sa, pa, xa;
string sb, pb, xb;
int main(){
    cin>>sa>>pa>>xa;
    cin>>sb>>pb>>xb;
    string ans=sa;
    if(pa == pb) ans="-1";
    if(pa.size()<pb.size()){
        ans = sb;
    }else if(pa.size()==pb.size() && pa<pb){
        ans = sb;
    }
    p(ans);
    return 0;
}