Problem Statement

Given is a $2 \times 2$ matrix $A = \begin{bmatrix} a & b \\ c & d \end{bmatrix}$. The determinant of $A$ can be found as $ad-bc$. Find it.

Constraints

• All values in input are integers.
• $-100 \le a, b, c, d \le 100$

Input

Input is given from Standard Input in the following format:

a b
c d

Output

Print the answer as an integer.