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)

/*
    問題をよく読もう！
    論理的に考えよう！
    サンプルを確認しよう!
    絶対に諦めるな！
    工夫をしろ！

    Twitterは終わるまでログアウト！
    （間違えて解法をツイートしてはいけないから）

*/
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <cctype>
using namespace std;
#define rep(i, n) for(int i=0; i<n; ++i)
typedef long long ll;
//必要な宣言
#define MAX_N 1000

int main() {
  int A, B, C, D;
  cin >> A >> B >> C >> D;
  int time_A[100] = {};
  int time_B[100] = {};
  int cnt = 0;

  for(int i=A; i<B; ++i) {
    time_A[i] = 1;
  }

  for(int i=C; i<D; ++i) {
    time_B[i] = 1;
  }

  for(int i=0; i<100; ++i) {
    if(time_A[i] == 1 && time_B[i] == 1)
      ++cnt;
  }

  cout << cnt << endl;

  return 0;
}