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 Rust (1.15.1) (judge verdict: Wrong Answer)

use std::io;

fn gets() -> String {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).ok();
    return buf
}

fn main() {
    let line = gets();
    let mut it = line.split_whitespace().map(|n| n.parse::<i64>().unwrap());
    let (a, b, c, d) = (it.next().unwrap(), it.next().unwrap(), it.next().unwrap(), it.next().unwrap());
    let ret;
    if b < c || d < a {
       ret = 0;
    } else if b == c {
        ret = 1;
    } else if a < c && d < b {
       ret = d - c;
    } else if a < c && d > b {
        ret = b - c;
    } else  {
        ret = b - a;
    }
    println!("{}", ret);
}