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)

/*
   	##############################
	## Author: Pratyush Gaurav ###
	## College: NIT ROURKELA #####
	##############################

	Bruce Wayne: I wanted to save Gotham. I failed.
	Alfred Pennyworth: Why do we fall sir? So that we can learn to pick ourselves up.
*/

#include <bits/stdc++.h>
//========================================================================================================//
//========================================================================================================//
using namespace std;
//========================================================================================================//
typedef long long/*--------------------*/ll;
typedef long double/*------------------*/ld;
typedef unsigned long long/*-----------*/ull;
typedef pair<ll, ll >/*----------------*/pll;
typedef std::vector<pll >/*------------*/vpll;
//========================================================================================================//
#define rep(i,a,b)/*-------------------*/for(i=a;i<b;i++)
#define repr(i,a,b)/*------------------*/for(i=a;i>=b;i--)
//========================================================================================================//
#define lb/*---------------------------*/lower_bound
#define ub/*---------------------------*/upper_bound
#define pb/*---------------------------*/push_back
#define popb/*-------------------------*/pop_back
#define mem(a,b)/*---------------------*/memset(a,b,sizeof(a))
#define sz/*---------------------------*/size()
#define MP/*---------------------------*/make_pair
#define bs/*---------------------------*/binary_search
#define gcd(a, b)/*--------------------*/__gcd(a, b)
#define lcm(a, b)/*--------------------*/((a)*((b)/gcd(a,b)))
#define sqr(x)/*-----------------------*/(x)*(x)
#define all(a)/*-----------------------*/a.begin(),a.end()
//========================================================================================================//
#define ff/*---------------------------*/first
#define ss/*---------------------------*/second
#define Vit/*--------------------------*/std::vector<ll>:: iterator
#define Sit/*--------------------------*/std::set<ll>:: iterator
#define Mit/*--------------------------*/std::map<ll,ll>:: iterator
//========================================================================================================//
#define endl/*-------------------------*/'\n'
//========================================================================================================//
#define inf/*--------------------------*/2e9
#define MOD/*--------------------------*/1000000007
//========================================================================================================//
void boost()
{
	std::ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
}
//========================================================================================================//
template<class T> bool is_prime(T n) { if((n%2==0 and n>2) or n<2 )	return false; for(T i=3;i*i<=n;i+=2){ if(n%i==0) return false;}return true;}
//========================================================================================================//
void solve()
{
	/*THE CODE GOES IN HERE*/
        std::vector<ll> v(101,0);
        ll a,b,c,d,ans = 0;
        cin >> a >> b >> c >> d;
        ll i;
        rep(i,a,b)
        {
                v[i]++;
        }
        rep(i,c,d)
        {
                v[i]++;
        }
        rep(i,0,101)
        {
                if(v[i] == 2)
                        ans++;
        }
        cout << ans << endl;

}
//========================================================================================================//
int main()
{
	//freopen("input.txt","r",stdin);
	//freopen("output.txt","w",stdout);
	boost();

	ll t;
	t=1;
	//cin>>t;
	while(t--)
		solve();
	return 0;
}