#include<bits/stdc++.h>
using namespace std;
string a,b;
int main(){
	cin>>a>>b;
	int lena=a.size(),lenb=b.size();
	if(lena>lenb){cout<<a;return 0;}
	if(lena<lenb){cout<<b;return 0;}
	for(int i=0;i<lena;i++){
		if(a[i]=='4'&&b[i]=='7'){cout<<a;return 0;}
		if(b[i]=='4'&&a[i]=='7'){cout<<b;return 0;}
		if(a[i]>b[i]){cout<<a;return 0;}
		if(b[i]>a[i]){cout<<b;return 0;}
	}
	return 0;
}