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.

Sample Input 1

1 2
3 4

Sample Output 1

-2

The determinant of \\begin{bmatrix} 1 & 2 \\\\ 3 & 4 \\end{bmatrix} is $1 \\times 4 - 2 \\times 3 = -2$.

Sample Input 2

0 -1
1 0

Sample Output 2

1

Sample Input 3

100 100
100 100

Sample Output 3

0