#include <iostream>

using namespace std;

int v[5];

int main()
{
    int a, b, c, d, nr1=1, nr2=1, i;

    cin>>a>>b;

    if(a>b)
        {v[1]=a; v[3]=b;}
    else
        {v[1]=b; v[3]=a;}

    cin>>c>>d;

    if(c>d)
        {v[2]=c; v[4]=d;}
    else
        {v[2]=d; v[4]=c;}

   cout<<v[1]*v[2]+v[3]*v[4];


}