Score : $100$ points

Problem Statement

We have a number line. Takahashi painted some parts of this line, as follows:

• First, he painted the part from $X=L_1$ to $X=R_1$ red.
• Next, he painted the part from $X=L_2$ to $X=R_2$ blue.

Find the length of the part of the line painted both red and blue.

Constraints

• $0\leq L_1
• $0\leq L_2
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

$L_1$ $R_1$ $L_2$ $R_2$

Output

Print the length of the part of the line painted both red and blue, as an integer.

0 3 1 5

2

The part from $X=0$ to $X=3$ is painted red, and the part from $X=1$ to $X=5$ is painted blue.

Thus, the part from $X=1$ to $X=3$ is painted both red and blue, and its length is $2$.

0 1 4 5

0

No part is painted both red and blue.

0 3 3 7

0

If the part painted red and the part painted blue are adjacent to each other, the length of the part painted both red and blue is $0$.