Problem Statement

Alice and Bob are controlling a robot. They each have one switch that controls the robot.
Alice started holding down her button ~A~ second after the start-up of the robot, and released her button ~B~ second after the start-up.
Bob started holding down his button ~C~ second after the start-up, and released his button ~D~ second after the start-up.
For how many seconds both Alice and Bob were holding down their buttons?

Constraints

• ~0≤A<B≤100~ </li>
• ~0≤C<D≤100~ </li>
• All input values are integers.

Input

Input is given from Standard Input in the following format:

~A~ ~B~ ~C~ ~D~

Output

Print the length of the duration (in seconds) in which both Alice and Bob were holding down their buttons.

Sample Input 1

0 75 25 100

Sample Output 1

50

Alice started holding down her button ~0~ second after the start-up of the robot, and released her button ~75~ second after the start-up.
Bob started holding down his button ~25~ second after the start-up, and released his button ~100~ second after the start-up.
Therefore, the time when both of them were holding down their buttons, is the ~50~ seconds from ~25~ seconds after the start-up to ~75~ seconds after the start-up.

Sample Input 2

0 33 66 99

Sample Output 2

0

Alice and Bob were not holding their buttons at the same time, so the answer is zero seconds.

Sample Input 3

10 90 20 80

Sample Output 3

60