#include <iostream>

using namespace std;

int main()
{
    int a[5],i,aux,j;
    cin>>a[1]>>a[2]>>a[3]>>a[4];
    for(i=1;i<=4;i++)
        for(j=i+1;j<=4;j++)
            if (a[i]>a[j])
                {
                    aux=a[i];
                    a[i]=a[j];
                    a[j]=aux;
                }
    aux=(a[1]*a[2])+(a[3]*a[4]);
    cout<<aux;

    return 0;
}