#include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <string>
#include <tuple>
#include <functional>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <map>
#include <random>
//#include "toollib.h"
#define INT_MAX 2147483647
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#pragma warning (disable:4018)

using namespace std;
typedef long long int lint;

typedef struct {
	int x;
	int y;
}coordinate;

//***** Main Program *****

//aが大きければ-1
int compare_large_numbers(string a, string b) {
	if (a.length() < b.length()) return 1;
	else if (a.length() > b.length()) return -1;
	else {
		int ret = 0;
		Loop(i, a.length()) {
			if (a[i] == '7'&&b[i] == '4') {
				ret = 1;
				break;
			}
			else if (a[i] == '4'&&b[i] == '7') {
				ret = -1;
				break;
			}
			else {
				if (a[i] < b[i]) {
					ret = 1;
					break;
				}
				else if (a[i]>b[i]) {
					ret = -1;
					break;
				}
			}
		}
		return ret;
	}
}

int main() {
	string A, B;
	cin >> A >> B;
	int judge = compare_large_numbers(A, B);
	if (judge == -1) cout << A << endl;
	else cout << B << endl;
	return 0;
}