#include <iostream>

using namespace std;

int v[6];

void QuickSort (int l, int r)
{
	int pv = v[(l + r) / 2], i = l, j = r;
	while (i <= j)
	{
		while (v[i] < pv) ++i;
		while (v[j] > pv) --j;
		if (i <= j)
		{
			int aux = v[i];
			v[i] = v[j];
			v[j] = aux;

			++i;
			--j;
		}
	}
	if (l < j) QuickSort (l, j);
	if (i < r) QuickSort (i, r);
}

int main ()
{
	for (int i = 1; i <= 4; ++i)
		cin >> v[i];
	QuickSort (1, 4);
	cout << v[4] * v[3] + v[2] * v[1] << "\n";
	return 0;
}