#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())


int cmp(const string &s,const string &t){
	if(s.size()>t.size())return 1;
	if(s.size()<t.size())return -1;
	rep(i,s.size()){
		if(s[i]>t[i])return 1;
		if(s[i]<t[i])return -1;		
	}
	return 0;
}

int main(){
	string s1,s2,p1,p2;
	char x1,x2;
	cin>>s1>>p1>>x1;cin.ignore(1);
	cin>>s2>>p2>>x2;
	int c=cmp(p1,p2);
	cout<<(c==1?s1:c==0?"-1":s2)<<endl;
	return 0;
}