#include <iostream>
#include <algorithm>
using namespace std;

int sum,v[10],i;

int main()
{
    for (i=1;i<=4;i++)
        cin>>v[i];
    sort(v+1,v+5);
    sum=v[1]*v[2]+v[3]*v[4];
    cout<<sum;
    return 0;
}