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 _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define rrep(i,n) for (int i=(n-1);i >= 0;i--)
#define all(v) v.begin(),v.end()
#define sz(v) (int)((v).size())
#define MAX(v) *max_element(all(v))
#define MIN(v) *min_element(all(v))
using namespace std; using ll = long long; using P = pair<int,int>;
using vl = vector<ll>; using vvl = vector<vl>;
inline void IN(void){return;}
template <typename First, typename... Rest>
void IN(First& first, Rest&... rest){cin >> first;IN(rest...);return;}
template<class T>bool chmax(T &a, const T &b) {if(a<b){a=b; return 1;} return 0;}
template<class T>bool chmin(T &a, const T &b) {if(b<a){a=b; return 1;} return 0;}
const ll INF = 1LL << 60;
const int dx[8] = {1,0,-1,0,1,1,-1,-1}; const int dy[8] = {0,1,0,-1,1,1,-1,-1};

int main(){
    cin.tie(0); ios::sync_with_stdio(false);
    int a,b,c,d;
    IN(a,b,c,d);
    int ans,start,end;
    start = max(a,c);
    end = min(b,d);
    if(start < end) ans = end - start;
    else ans = 0;
    cout << ans << endl;
}