Problem:
Score : 200 points

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

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 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

Solution in Python (3.4.3) (judge verdict: Accepted)

a_list = list(map(int, input().split()))
a, b, c, d = a_list[0], a_list[1], a_list[2], a_list[3]

start = 0
alice_time = (a, b)
bob_time = (c, d)

max_end = max(b, d)
alice_zone = [0] * max_end
bob_zone = [0] * max_end
alice_zone[a:b] = [1] * len(alice_zone[a:b])
bob_zone[c:d] = [1] * len(bob_zone[c:d])

kasanari_zone = [alice * bob for alice, bob, in zip(alice_zone, bob_zone)]
print(sum(kasanari_zone))