#include <iostream>
#include <algorithm>

using namespace std;

int A, B, C, D;

int main()
{
	cin >> A >> B >> C >> D;
	
	int res1 = A * B + C * D;
	int res2 = A * C + B * D;
	int res3 = A * D + B * C;
	
	cout << max(res1, max(res2, res3)) << '\n';
}