#include <algorithm>
#include <cstdio>

using namespace std;

int main()
{
    //freopen("input", "r", stdin);
    //freopen("output", "w", stdout);
    int a[5], smax=0, i;
    for(i=1;i<5;i++) scanf("%d", &a[i]);
    sort(a+1, a+5);
    do
    {
        smax=max(smax, a[1]*a[2]+a[3]*a[4]);
    }
    while(next_permutation(a+1, a+5));
    printf("%d", smax);
}