#include <iostream>
#include <climits>

using namespace std;

int main(void)
{
	int a, b, c, d;
	int v[4];
	int i, j, k, m;
	int max = INT_MIN;
	int crt;

	cin >> a >> b >> c >> d;

	v[0] = a;
	v[1] = b;
	v[2] = c;
	v[3] = d;

	for (i = 0; i < 4; i++)
		for (j = 0; j < 4; j++)
			for (k = 0; k < 4; k++)
				for (m = 0; m < 4; m++) {
					if (i != j && i != k && i != m && j != m && j != k && k != m) {
						crt = v[i] * v[j] + v[k] * v[m];
						if (crt > max)
							max = crt;
					}
				}
	cout << max << endl;

	return 0;
}