F. Максимум

#include <bits/stdc++.h>

using namespace std;

const int inf = 1e9;

int main(){
    int a, b, c, d;
    cin >> a >> b >> c >> d;

    int ans = -inf;

    ans = max(ans, a * b + c * d);
    ans = max(ans, a * c + b * d);
    ans = max(ans, a * d + b * c);

    cout << ans << endl;
}