#include <iostream>

using namespace std;

int main()
{
    int a,b,c,d,k=0,kmax=0,aux,nr;
    cin>>a;
    cin>>b;
    cin>>c;
    cin>>d;
    aux=a*b;
    k+=aux;
    aux=c*d;
    k+=aux;
    kmax=k;
    nr=1;
    k=0;
    aux=a*c;
    k+=aux;
    aux=b*d;
    k+=aux;
    if(k>kmax)
        kmax=k;
    k=0;
    aux=a*d;
    k+=aux;
    aux=b*c;
    k+=aux;
    if(k>kmax)
        kmax=k;
    cout<<kmax;
    return 0;
}