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 Ruby (2.3.3) (judge verdict: Runtime Error)

#encoding: utf-8

intervalTime = STDIN.gets.split(" ").map(&:to_i);

def maxNum(a, c)
	if a < c then
		return c
	else
		return a
	end
	return 0
end

def minNum(b, d)
	if b < c then
		return b
	else
		return d
	end
end

def checkTime(min, max)
	if max > min then
		STDOUT.puts "0";
	else
		STDOUT.puts min - max;
	end
	return 0;
end

checkTime(minNum(intervalTime[1], intervalTime[3]), maxNum(intervalTime[0], intervalTime[2]));