#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int f(int x, int y) {
	if (x == 4 && y == 7) return 1;
	if (x == 7 && y == 4) return -1;
	if (x == y) return 0;
	if (x < y) return -1;
	if (x > y) return 1;
}

int main() {
	string A, B; cin >> A >> B;
	string a = A, b = B;
	for (; A.length() < 10; A = '0' + A);
	for (; B.length() < 10; B = '0' + B);
	for (int i = 0; i < 10; i++) {
		int x = f(A[i] - '0', B[i] - '0');
		if (x == -1) {
			cout << b << endl;
			return 0;
		}
		if (x == 1) {
			cout << a << endl;
			return 0;
		}
	}
}