https://contest.yandex.ru/contest/71291/problems/C/

C. Flight Speed

Time limit: 1 second
Memory limit: 64 MB
Input: standard input or input.txt
Output: standard output or output.txt

Arman and his assistants are flying from Earth to a space station to repair the gravity matrix.
The rocket’s time–distance graph (time x in hours since launch, distance y in kilometers from Earth) follows a parabola: [ y = a x^2 + b x + c. ] They want to know the rocket’s speed exactly d hours after launch.

Input
Real numbers a, b, c, and d on separate lines.
Constraints: (0 < a, b, c, d < 1000).

Output
Print the answer to the problem.

Sample Input

10 4.65116 7.178 12

Sample Output

244.65116