#include<iostream>
#include<string>

using namespace std;

int main(){

	string A,B;

	cin>>A>>B;

	if(A.size()>B.size()) cout<<A<<endl;
	else if(A.size()<B.size()) cout<<B<<endl;
	else{
		for(int i=0;i<A.size();i++){
			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 if(A[i]<B[i]) cout<<B<<endl;
			if(A[i]!=B[i]) break;
		}
	}
}