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
- 0≤C<D≤100
- 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-----
0 75 25 100

-----Sample Output-----
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.

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