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)

#include "bits/stdc++.h"
#define repr(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define repr_inv(i,a,b) for(int i=(int)(a);i>=(int)(b);i--)
#define rep(i,n) repr(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define MOD 1000000007
#define PI 3.1415926535
using namespace std;
string YN(bool y) { return (y?"YES":"NO"); }
string yn(bool y) { return (y?"Yes":"No"); }
string ON(bool y) { return (y?"OK":"NG"); }
int main(void)
{
	int a, b, c, d, ans=0;

	cin>>a>>b>>c>>d;

	vector<bool> aa(100, false), bb(100, false);

	repr(i, a, b) aa[i]=true;

	repr(i, c, d) bb[i]=true;

	rep(i, 100){
		if(aa[i]&&bb[i]) ans++;
	}
	cout<<ans<<endl;
}