#include <cstdio>

using namespace std;

int a, b, c, d, s;

int main()
{
    scanf("%d %d %d %d\n", &a, &b, &c, &d);
    s = a*b + c*d;
    if (a*c + b*d > s)
        s = a*c + b*d;

    printf("%d", s);
    return 0;
}