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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
class Program
{
    static void Main(string[] args)
    {
            // 入力
            string[] sS = Console.ReadLine().Trim().Split(' ');
            int iA = int.Parse(sS[0]);
            int iB = int.Parse(sS[1]);
            int iC = int.Parse(sS[2]);
            int iD = int.Parse(sS[3]);

            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            sw.Start();

            // 解析
            int iOut = 0;                                                           // 場合分け6パターン
            if (iB <= iC) { }                                                       // 重なりなし
            if (iA <= iC && iC <= iB && iB <= iD)             { iOut = iB - iC; }   // 重なりあり
            if (iA <= iC && iC <= iB && iA <= iD && iD <= iB) { iOut = iD - iC; }   // 含有
            if (iD <= iA) { }                                                       // 重なりなし
            if (iC <= iA && iA <= iD && iD <= iB)             { iOut = iD - iA; }   // 重なりあり
            if (iC <= iA && iA <= iD && iC <= iB && iB <= iD) { iOut = iB - iA; }   // 含有

            //出力
            Console.WriteLine("{0}", iOut.ToString().Trim());

            sw.Stop();
#if DEBUG
            Console.WriteLine();
            Console.WriteLine("{0}", sw.Elapsed.ToString());
            Console.WriteLine("続行するには何かキーを押してください．．．");
            Console.ReadKey();
#endif
    }
}