#include <iostream>
#include <string>
#include <cstring>
#include <stack>
using namespace std;

bool comp(int n, int m)
{
	if (n == 4 && m == 7) return true;
	if (n == 7 && m == 4) return false;
	if (n > m) return true;
	return false;
}

int main()
{
	long long a, b,aa,bb;

	cin >> a >> b;
        aa = a;
        bb = b; 

	stack<int> sa, sb;

	while (a > 0 || b > 0) {
		sa.push(a % 10);
		a /= 10;	
		sb.push(b % 10);
		b /= 10;
	}

	while (!sa.empty()) {
		if (sa.top() == sb.top()) {
			sa.pop();
			sb.pop();
		}
		else if (comp(sa.top(), sb.top())) {
			cout << aa << endl;
			return 0;
		}
		else {
			cout << bb << endl;
			return 0;
		}
	}

	return 0;
}