#include <iostream>
#include <vector>
#include <string>
#include <array>
#include <queue>
#include <deque>
#include <set>
#include <list>
#include <map>
#include <stack>
#include <utility>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <cstring>
#include <climits>
#include <bitset>
#include <random>
#include <functional>
#include <sstream>
#include <iomanip>

using namespace std;

#define _CRT_SECURE_NO_WARNINGS
#define REP(i, n) for(int i=0; i<(n); i++)
#define FOR(i, m, n) for(int i=(m);i<(n);i++)
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(),(x).end()
#define SORT(x) sort((x).begin(),(x).end())
#define REVE(x) reverse((x).begin(),(x).end())
#define MP make_pair
#define PB push_back

typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<vector<int>> VVI;
typedef pair<int, int> PII;
typedef long long LL;

int main() {
	string sa, sb, pa, pb;
	char xa, xb;
	cin >> sa >> pa >> xa >> sb >> pb >> xb;
	int ans;
	if (SZ(pa) > SZ(pb))ans = 1;
	if (SZ(pa) < SZ(pb))ans = 2;
	if (SZ(pa) == SZ(pb)) {
		if (pa > pb)ans = 1;
		if (pa < pb)ans = 2;
		if (pa == pb)ans = 3;
	}

	if (ans == 1)cout << sa;
	if (ans == 2)cout << sb;
	if (ans == 3)cout << -1;
	puts("");
}