#include <iostream>

using namespace std;

int main()
{
    int a, b, c, d, sum1, sum2, v[7];
    cin>>a>>b>>c>>d;
    v[1]=a*b;
    v[2]=a*c;
    v[3]=a*d;
    v[4]=b*c;
    v[5]=b*d;
    v[6]=c*d;
    sum1=v[1]+v[6];
    sum2=v[2]+v[5];
    if(sum1>sum2) sum2=sum1;
    sum1=v[3]+v[4];
    if(sum1>sum2) sum2=sum1;
    cout<<sum2;
    return 0;
}