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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
# 整数の入力
fscanf(STDIN, "%d %d %d %d", $a, $b, $c, $d);

echo calc($a, $b, $c, $d) ;
function calc($a, $b, $c, $d) {
  if($b <= $c) return 0;
  if($d <= $a) return 0;

  if($a <= $c && $b <= $d) return ($b - $c);
  if($a <= $c && $d <= $b) return ($d - $c);
  if($c <= $a && $d <= $b) return ($c - $b);
  if($c <= $a && $b <= $d) return ($b - $a);
  
  return -1;
}