#include <iostream>
#include <algorithm>

using namespace std;
int compare (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}
int main()
{
    int v[4];
    for(int i = 0; i<4; ++i)
    {
        cin>>v[i];
    }
    qsort(v,4,sizeof(int),compare);
    int result = v[3]*v[2]+v[1]*v[0];
    cout<<result;
    return 0;
}