output_description: Print the length of the duration (in seconds) in which both Alice and Bob were
  holding down their buttons.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      A B C D
attempt: a,b,c,d = map(int, input().split())
  if a > c:
      a,b,c,d = c,d,a,b
  if b < c:print(0)
  elif b => c and b < d:print(b-c)
  else : print(d-c)
problem_description: 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?
samples: [{"input": "0 75 25 100", "output": "50\n    \n\nAlice started holding down her button 0 second after the start-up of the\nrobot, and released her button 75 second after the start-up.  \nBob started holding down his button 25 second after the start-up, and released\nhis button 100 second after the start-up.  \nTherefore, the time when both of them were holding down their buttons, is the\n50 seconds from 25 seconds after the start-up to 75 seconds after the start-\nup.\n\n* * *"}, {"input": "0 33 66 99", "output": "0\n    \n\nAlice and Bob were not holding their buttons at the same time, so the answer\nis zero seconds.\n\n* * *"}, {"input": "10 90 20 80", "output": "60"}]