#include <bits/stdc++.h>

using namespace std;

int arr[4]={0,1,2,3};
int arr2[4];

int main()
{
cin >> arr2[0] >> arr2[1] >> arr2[2] >> arr2[3];
int maxi=0;
do
{
maxi=max(maxi,arr2[arr[0]]*arr2[arr[1]]+rr2[arr[2]]*arr2[arr[3]]);
}while(next_permutation(arr,arr+4));
cout << maxi << endl;
}