Line Slope

Version: Phuoc Hung OJ Extended

Problem Statement

A line passes through points $A(x_1,y_1)$ and $B(x_2,y_2)$ with distinct $x$-coordinates. Its slope is $k=\dfrac{y_2-y_1}{x_2-x_1}$. The input guarantees $x_1\ne x_2$. Compute the slope and print exactly 6 digits after the decimal point.

Input

The only line contains real numbers $x_1$, $y_1$, $x_2$, $y_2$ giving the two points in order.

Output

Print slope $k$ with exactly 6 decimal places.

Subtasks

• Subtask 1 (100 points): All coordinates are finite; $x_1\ne x_2$.

Examples

Example 1

Input

0 0 2 4

Output

2.000000

Explanation. The vertical difference is 4 and the horizontal difference is 2. Their quotient is 2; six-decimal formatting gives 2.000000.

Example 2

Input

1 3 4 0

Output

-1.000000

Explanation. The vertical difference is -3 and the horizontal difference is 3. Their quotient is -1; six-decimal formatting gives -1.000000.

Example 3

Input

-1 -1 1 0

Output

0.500000

Explanation. The vertical difference is 1 and the horizontal difference is 2. Their quotient is 0.5; six-decimal formatting gives 0.500000.