#include <iostream>

#include <cmath>

using namespace std;

int main() {

double f,a, b, c, x;

cin >> c >> a >> b >> x;

if (c < 0 && a != 0) {

 f = ((-a * pow(x, 3) - b) / c);

}

else if (c > 0 && a == 0) {

 f = (x - pow(a, 3) / (-c));

}

else {

 f = a * x + 5 * b;

}

cout << f;

return 0;

}