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++14 (GCC 5.4.1) (judge verdict: Accepted)

//============================================================================
// Name        : atcoder.cpp
// Author      :
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
using namespace std;
int A,B,C,D;
int M;
int main(){
	cin>>A>>B>>C>>D;

	int R,S;

	if(A<C)R=C;
	if(A>C)R=A;
	if(B>D)S=D;
	if(D>B)S=B;

	if(B<C){
		M=0;
	}else if(B==C){
		M=0;
	}else if(B==0||D==0){
		M=0;
	}else if(C<A&&D<A){
		M=0;
	}else{
		M=(S-R);
	}
	cout<<M<<endl;


	return 0;
}