#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD 1000000007
using namespace std;
typedef long long LL;
typedef vector<int> VI;

int main() {
	string sa, sb, pa, pb;
	char xa, xb;
	cin >> sa >> pa >> xa;
	cin >> sb >> pb >> xb;
	string ans;
	int la, lb;
	la = SZ(pa);
	lb = SZ(pb);
	if (la != lb) ans = (la > lb) ? sa : sb;
	if (la == lb) {
		REP(i, la) {
			if (pa[i] != pb[i]) {
				ans = (pa[i] > pb[i]) ? sa : sb;
				break;
			}
		}
	}
	if (pa == pb) {
		cout << -1 << endl;
		return 0;
	}
	cout << ans << endl;
	return 0;
}