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 C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>


int main()
{
    int a, b, c, d;
    int ans;

    int division_right;
    
    scanf("%d %d %d %d", &a, &b, &c, &d);

    if (a <= c)
    {
	// cが区間の左端？
	// a---b  c---d
	
	// 区間は重なっている？
	if (b < c)
	{
	    ans = 0;
	}
	else
	{
	    if (b <= d)      // a---c--b---d
	    {
		division_right = b;
	    }
	    else             // a---c--d---b
	    {
		division_right = d;
	    }
	    ans = division_right - c;
	}
    }
    else
    {
	// aが区間の左端？
	// c-----d a-----b

	// 区間は重なっている？
	if (d < a)
	{
	    ans = 0;
	}
	else
	{
	    if (d <= b)     // c---a--d--b
	    {
		division_right = d;
	    }
	    else            // c---a--b---d
	    {
		division_right = b;
	    }
	    ans = division_right - a;
	}
    }

    printf("%d\n", ans);

    return 0;
}