#include <cstdio>
#include <algorithm>

using namespace std;

int main()
{
	int T[10];
	int Mx=0;
	int perm[10]={0, 1, 2, 3, 4};
	scanf ("%d%d%d%d", T+1, T+2, T+3, T+4);
	do
	{
		int sum=T[perm[1]]*T[perm[2]]+T[perm[3]]*T[perm[4]];
		Mx=max (sum, Mx);
	}
	while (next_permutation(perm+1, perm+5));
	printf ("%d\n", Mx);
	return 0;
}