#include <cstdio>

using namespace std;

int a,b,c,d,maxx;

int main()
{
    scanf ("%d %d %d %d",&a,&b,&c,&d);
    maxx = 0;
    if (a*b+c*d > maxx) maxx = a*b+c*d;
    if (a*c+b*d > maxx) maxx = a*c+b*d;
    if (a*d+c*b > maxx) maxx = a*d+c*b;
    printf ("%d\n",maxx);
    return 0;
}