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

int v[7];

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