#include <cstdio>

using namespace std;
void quicksort(short v[], short stanga, short dreapta)
{
   short i, j, mijloc, aux;
   i=stanga;
   j=dreapta;
   mijloc=v[(stanga+dreapta)/2];
  while(i<=j)
  {
   while(v[i]<mijloc)
      i++;
   while(v[j]>mijloc)
      j--;
    if(i<=j)
    {
       aux=v[i];
       v[i]=v[j];
       v[j]=aux;
       i++;
       j--;
     }
  }
 if(stanga<j)
   quicksort(v, stanga, j);
 if(i<dreapta)
   quicksort(v, i, dreapta);

}
int main()
{
    short a[4];
    scanf("%hd%hd%hd%hd",&a[0],&a[1],&a[2],&a[3]);
    quicksort(a,0,3);
    printf("%hd\n",a[0]*a[1]+a[2]*a[3]);
    return 0;
}