#include <iostream>
#include <algorithm>

using namespace std;
int v[5] = {0,1,2,3,4};
int val[5];

int main()
{
    int best = -1;

    cin >> val[1] >> val[2] >> val[3] >> val[4];

    do{
        best = max ( best ,val[v[1]] * val[v[2]] + val[v[3]] * val[v[4]]);
    }while(next_permutation(val+1,val+5));

    cout << best;

    return 0;
}