#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <iomanip>
using namespace std;

#define ll long long
#define INF (1 << 30)
#define INFLL (1LL << 60)

int main() {
	string a,b;
	cin >> a >> b;
	if(a.size() == b.size()){
		for(int i = 0;i < a.size();i++){
			if(a[i] == b[i]){
				continue;
			}else{
				if(a[i] == '4' && b[i] == '7'){
					cout << a << endl;
				}else if(a[i] == '7' && b[i] == '4'){
					cout << b << endl;
				}else if(a[i] > b[i]){
					cout << a << endl;
				}else{
					cout << b << endl;
				}
				break;
			}
		}
	}else if(a.size() > b.size()){
		cout << a << endl;
	}else if(a.size() < b.size()){
		cout << b << endl;
	}
	return 0;
}