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 PHP (5.6.30) (judge verdict: Accepted)

<?php  

$stdin = trim(fgets(STDIN));  
$number = array();
$number = explode(" ",$stdin);
$a1 = (int)$number[0];
$a2 = (int)$number[1];
$b1 = (int)$number[2];
$b2 = (int)$number[3];
$c1 = ($a1 > $b1) ? $a1 : $b1;
$c2 = ($a2 < $b2) ? $a2 : $b2;
$c3 = (int)($c2 - $c1); 
if($c3 < 0){
	echo "0";
}else{
	echo $c2 - $c1 ;
}
?>