#include <fstream>

using namespace std;
ifstream in("Spell.in");
ofstream out("Spell.out");

int main()
{
 int a,b,c,d,caz1,caz2,caz3,vrajMax;
 in >>a;in>>b;in>>c;in>>d;
 caz1=(a*b)+(c*d);
 caz2=(a*c)+(b*d);
 caz3=(a*d)+(b*c);
 vrajMax=caz1;
 if(caz2>vrajMax){
 vrajMax=caz2;
 }
  if(caz3>vrajMax){
 vrajMax=caz3;
 }
 out << vrajMax;
}