#include <bits/stdc++.h>
using namespace std;
long long mod = 1000003;

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