#include <cstdio>
#include <algorithm>

using namespace std;

int a[10];
int n = 4;
int main() {
    //freopen ("a.in", "r", stdin);
    scanf ("%d %d %d %d", &a[1], &a[2], &a[3], &a[4]);
    int smax = -0x3f3f3f3f, s;
    do {
        s = a[1] * a[2] + a[3] * a[4];
        if (smax < s)
            smax = s;
    } while (next_permutation(a + 1, a + n + 1));
    printf ("%d\n", smax);
}