#include <bits/stdc++.h>

using namespace std;

#define INF 2000000000
#define MOD 1000000007
typedef long long ll;
typedef pair<int, int> P;


int main()
{
	int a;
	int b;
	cin >> a >> b;

	string as = to_string(a);
	string bs = to_string(b);

	if (as.size()>bs.size()) {
		cout << a << "\n";
		return 0;
	} else if (as.size()<bs.size()) {
		cout << b << "\n";
		return 0;
	}

	for (int i = 0; i < as.size(); i++) {
		if (as[i]==bs[i]) {
			continue;
		} else if (as[i]=='4'&&bs[i]=='7') {
			cout << a << "\n";
			return 0;
		} else if (bs[i]=='4'&&as[i]=='7') {
			cout << b << "\n";
			return 0;
		} else if (as[i]>bs[i]) {
			cout << a << "\n";
			return 0;
		} else if (as[i]<bs[i]) {
			cout << b << "\n";
			return 0;
		}
	}
}