#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>
#include <time.h>
#include <numeric>
using namespace std;
//#define int long long
#define rep(i,s,n) for(int i = s;i<n;i++)
#define repe(i,s,n) for(int i = s;i<=n;i++)
#define rrep(i,s,n) for(int i = (n)-1;i>=(s);i--)
#define all(v) (v).begin(),(v).end()
#define pb push_back
#define fi first
#define se second
#define chmin(a,b) a=min((a),(b))
#define chmax(a,b) a=max((a),(b))
#define l1 list[index]
#define l2 list[index - 1]
#define l3 list[index + 1]
#define iif(i,j) ((i<0 && j<0) || (i>0 && j>0)) ? true : false 
typedef long long ll;
typedef pair<int, int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
typedef pair<pint, int> P1;
typedef pair<int, pint> P2;
typedef pair<pint, pint> PP;
static const ll maxLL = (ll)1 << 62;
const ll MOD = 1000000007;
const ll INF = 1e18;
const double PI = 3.14159265359;
int ca[12] = { 31,28,31,30,31,30,31,31,30,31,30,31 };



signed main() {
	string s1, s2, s1b, s2b;
	string keta1, keta2;

	cin >> s1 >> keta1 >> s1b;
	cin >> s2 >> keta2 >> s2b;

	if (keta1.length() < keta2.length()) {
		cout << s2 << endl;
	}
	else if (keta1.length() > keta2.length()) {
		cout << s1 << endl;
	}
	else {
		int flag = 0;
		for (int i = 0; i < keta1.length(); i++) {
			if (keta1[i] != keta2[i]) {
				if (keta1[i] > keta2[i]) {
					flag = 1;
				}
				else {
					flag = 2;
				}
				break;
			}
		}

		if (flag == 0) {
			cout << -1 << endl;
		}
		else if (flag == 1) {
			cout << s1 << endl;
		}
		else {
			cout << s2 << endl;
		}
	}

	return 0;
}