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# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var list = new List<int>();
            var a = Console.Read();
            var b = Console.Read();
            var c = Console.Read();
            var d = Console.Read();

            list.Add(a);
            list.Add(b);
            list.Add(c);
            list.Add(d);



            if (b <= c || d <= a)
            {
                Console.WriteLine(0);
            }
            else if (a <= c && c <= d && d <= b)
            {
                Console.WriteLine(d-c);
            }
            else if (c <= a && a <= b && b <= d)
            {
                Console.WriteLine(b-a);
            }
            else if (a <= c && c <= b && b <= d)
            {
                Console.WriteLine(b-c);
            }
            else if (c <= a && a <= d && d <= b)
            {
                Console.WriteLine(d-a);
            }
        }
    }
}