#include <bits/stdc++.h>
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(unsigned 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(B[i]<A[i]) cout << B << endl;
	         if(A[i]!=B[i]) break;
    	}
    }
}