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