#include <algorithm>
#include <iostream>

using namespace std;

const int nmax= 4;

int v[nmax+1];

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

    return 0;
}