#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>



using namespace std;




int main() {

	string a,b;
	cin>>a>>b;
	long long int x=0,y=0;
	for(int i=0;i<a.size();i++){
		x*=10;
		if(a[i]=='7')x+=4;
		else if(a[i]=='4')x+=7;
		else x+=a[i]-'0';
	}
	for(int i=0;i<b.size();i++){
		y*=10;
		if(b[i]=='7')y+=4;
		else if(b[i]=='4')y+=7;
		else y+=b[i]-'0';
	}
	if(x>y)cout<<a<<endl;
	else cout<<b<<endl;
	
	

	return 0;
}