#include <fstream>
//spell
using namespace std;

int main()
{
    int a, b, c, d;
    int sum1, sum2;
    fscanf(stdin,"%d%d%d%d", &a, &b, &c, &d);
    sum1 = a*b + c*d;
    sum2 = a*c + d*b;
    if (sum2 > sum1)
        sum1 = sum2;

    sum2 = a*d + c*b;
    if (sum2 > sum1)
        sum1 = sum2;
    fprintf(stdout, "%d", sum1);
    return 0;
}