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: Wrong Answer)

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

    if not (0 <= a and a < b and b <= 100 and 0 <= c and c < d and d <= 100):
        return
    if not (isinstance(a, int) and isinstance(b, int) and isinstance(c, int) and isinstance(d, int)):
        return
    
    if(b <= c or d <= a):
        print(0)
    elif(c < b and b <= d):
        print(b - c)
    elif(a <= c and d <= b):
        print(d - c)
    elif(a < d and d <= b):
        print(d - a)
    elif(c <= a and b <= d):
        print(b - a)


if __name__ == "__main__":
    main()