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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

• $0\leq L_1<R_1\leq 100$
• $0\leq L_2<R_2\leq 100$
• 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.

### Sample Input 1

0 3 1 5


### Sample Output 1

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 $2$.

### Sample Input 2

0 1 4 5


### Sample Output 2

0


No part is painted both red and blue.

### Sample Input 3

0 3 3 7


### Sample Output 3

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 $0$.