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: Accepted)

fn read_line() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s
}

fn read<T: std::str::FromStr>() -> T where T::Err: std::fmt::Debug {
    read_line().trim().parse().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T>
where T::Err: std::fmt::Debug {
    read_line().split_whitespace().map(|s| s.parse().unwrap()).collect()
}

fn read2<T1: std::str::FromStr, T2: std::str::FromStr>() -> (T1, T2)
where T1::Err: std::fmt::Debug, T2::Err: std::fmt::Debug {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let mut splitted = s.split_whitespace();
    let v1: T1 = splitted.next().unwrap().parse().unwrap();
    let v2: T2 = splitted.next().unwrap().parse().unwrap();
    (v1, v2)
}

fn read3<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr>() -> (T1, T2, T3)
where T1::Err: std::fmt::Debug, T2::Err: std::fmt::Debug, T3::Err: std::fmt::Debug {
    let line = read_line();
    let mut splitted = line.split_whitespace();
    let v1: T1 = splitted.next().unwrap().parse().unwrap();
    let v2: T2 = splitted.next().unwrap().parse().unwrap();
    let v3: T3 = splitted.next().unwrap().parse().unwrap();
    (v1, v2, v3)
}

fn read4<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr, T4: std::str::FromStr>() -> (T1, T2, T3, T4)
where T1::Err: std::fmt::Debug, T2::Err: std::fmt::Debug, T3::Err: std::fmt::Debug, T4::Err: std::fmt::Debug {
    let line = read_line();
    let mut splitted = line.split_whitespace();
    let v1: T1 = splitted.next().unwrap().parse().unwrap();
    let v2: T2 = splitted.next().unwrap().parse().unwrap();
    let v3: T3 = splitted.next().unwrap().parse().unwrap();
    let v4: T4 = splitted.next().unwrap().parse().unwrap();
    (v1, v2, v3, v4)
}

use std::cmp;
fn main() {
    let (a, b, c, d): (i32, i32, i32, i32)  = read4();

    let begin = cmp::max(a, c);
    let end = cmp::min(b, d);
    let mut time = end - begin;
    if time < 0 {
        time = 0;
    }
    println!("{}", time);
}