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.

Input

Input is given from Standard Input in the following format:
a b
c d

Output

Print the answer as an integer.

Constraints

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

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

见题面 Input 部分

见题面 Output 部分