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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

program Project1;

{$APPTYPE CONSOLE}

uses
  SysUtils,Classes;
var
  d,a,h,w,i,j,count,x,y,sw,m,n,b,c,soeji,sum,max,k,min:Integer;
  //l:array[0..6] of Integer = (1,2,4,8,16,32,64);
  s,s123,s1,s2,s3:string;
  tf:Boolean;
  nyu:TStringList;
begin
  try
    { TODO -oUser -cConsole Main : ここにコードを記述してください }
    Read(a);
    Read(b);
    Read(c);
    Readln(d);

    sum:=(b+d-abs(b-d))div 2 - (a+c+abs(a-c))div 2;
    Writeln((sum+0+abs(sum-0))div 2);
    Readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.