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.

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.

Constraints

• $0\leq L_1<R_1\leq 100$
• $0\leq L_2<R_2\leq 100$
• All values in input are integers.

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.

见题面 Input 部分

见题面 Output 部分