#include<bits/stdc++.h>
using namespace std;


int main() {
    string A,B;
    cin >> A >> B;
    int a=(int)A.length(), b=(int)B.length();

    if(a==b){
        for(int i=0; i<a; i++){
            if(A[i]=='4' && B[i]=='7'){
                cout << A << endl;
                return 0;
            }
            else if(A[i]=='7' && B[i]=='4'){
                cout << B << endl;
                return 0;
            }
            else if(A[i]>B[i]){
                cout << A << endl;
                return 0;
            }
            else if(A[i]<B[i]){
                cout << B << endl;
                return 0;
            }
        }
    }
    else if(a>b){
        cout << A << endl;
    }
    else if(a<b){
        cout << B << endl;
    }

}