#include<iostream>
#include<algorithm>
#include<string>
#include<math.h>
#include<bitset>
#include <vector>
#include<bitset>
#include <iomanip>
#include <map>
#include <set>
#include <stack>
#include <deque>
#include <climits>
#include <queue>
using namespace std;

int main() {
	long long A, B;
	cin >> A >> B;
	string S = to_string(A);
	string T = to_string(B);
	int SS = S.size();
	int TT = T.size();
	if (SS > TT)cout << S<<endl;
	else if (TT > SS)cout << T<<endl;
	else {
		for (int i = 0; i < SS; i++) {
			if (S[i] == '4' && T[i] == '7') {
				cout << S << endl;
				break;
			}
			if (S[i] == '7' && T[i] == '4') {
				cout << T << endl;
				break;
			}
			if (S[i] - '0' > T[i] - '0') {
				cout << S << endl;
				break;
			}
			else if (S[i] - '0' < T[i] - '0') {
				cout << T << endl;
				break;
			}
		}
	}


}