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<cstdio>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<vector>
#include<queue>
#include<stack>
#include<map>
using namespace std;
#define FOR(i,s,e) for (int i=s;i<e;i++)
#define FOE(i,s,e) for (int i=s;i<=e;i++)
#define FOD(i,s,e) for (int i=s;i>=e;i--)
#define SET(a,e) memset(a,e,sizeof(a))
#define LL long long
#define LD long double
#define pb push_back
#define x first
#define y second
#define PII pair<int,int>
#define PLI pair<LL,int>
#define PIL pair<int,LL>
#define PLL pair<LL,LL>
#define eps 1e-9
#define mp make_pair

int a,b,c,d,r[105],ans;

int main () {
	scanf("%d%d%d%d",&a,&b,&c,&d);
	FOE(i,a,b-1) ++r[i];
	FOE(i,c,d-1) ++r[i];
	FOE(i,0,100) if (r[i]==2)++ans;
	printf("%d\n",ans);
	return 0;	
}