#include <iostream>

using namespace std;

int main()
{
    int x[5],i,aux,j;
    for (i=1;i<=4;i++) cin>>x[i];

    for (i=1;i<=4;i++)
        for (j=i+1;j<=4;j++)
            if(x[j]>x[i])
            {
                aux=x[i];
                x[i]=x[j];
                x[j]=aux;
            }
    cout<<x[1]*x[2]+x[3]*x[4];
    return 0;
}