Problem:
Score : 200 points

Problem Statement

We have A cards, each of which has an integer 1 written on it. Similarly, we also have B cards with 0s and C cards with -1s.

We will pick up K among these cards. What is the maximum possible sum of the numbers written on the cards chosen?

Constraints

All values in input are integers.

0 \leq A, B, C

1 \leq K \leq A + B + C \leq 2 \times 10^9

Input

Input is given from Standard Input in the following format:

A B C K

Output

Print the maximum possible sum of the numbers written on the cards chosen.

Sample Input 1

2 1 1 3

Sample Output 1

2

Consider picking up two cards with 1s and one card with a 0.
In this case, the sum of the numbers written on the cards is 2, which is the maximum possible value.

Sample Input 2

1 2 3 4

Sample Output 2

0

Sample Input 3

2000000000 0 0 2000000000

Sample Output 3

2000000000

Solution in Rust (1.42.0) (judge verdict: Accepted)

use input::{Input, ReadMode};

fn main() {
    let mut input = Input::new(ReadMode::Line);

    let a: i32 = input.parse();
    let b: i32 = input.parse();
    let _c: i32 = input.parse();
    let k: i32 = input.parse();

    let mut ans = a.min(k);
    let x = k - ans;
    if x > 0 && b < x {
        ans += b - x;
    }

    println!("{}", ans);
}

#[allow(dead_code)]
pub mod input {
    use std::io::{BufRead, Read};

    pub enum ReadMode {
        Full,
        Line,
    }

    pub struct Input<'a> {
        lock: std::io::StdinLock<'static>,
        iter: Option<std::str::SplitAsciiWhitespace<'a>>,
        mode: ReadMode,
    }

    impl<'a> Input<'a> {
        fn naive_read(&mut self) -> Option<std::str::SplitAsciiWhitespace<'a>> {
            let mut s = Box::leak(Box::new(String::new()));
            let res = match self.mode {
                ReadMode::Full => self.lock.read_to_string(&mut s),
                ReadMode::Line => self.lock.read_line(&mut s),
            };
            res.ok().expect("failed to read");
            Some(s.split_ascii_whitespace())
        }
        pub fn new(mode: ReadMode) -> Self {
            let lock = Box::leak(Box::new(std::io::stdin())).lock();
            let iter = None;
            Self { lock, iter, mode }
        }
        pub fn read_line(&mut self) -> String {
            let mut s = String::new();
            self.lock.read_line(&mut s).ok().expect("failed to read");
            s
        }
        pub fn parse<T: std::str::FromStr>(&mut self) -> T {
            match &mut self.iter {
                Some(iter) => {
                    let x = if let Some(x) = iter.next() {
                        x
                    } else {
                        self.iter = self.naive_read();
                        self.iter.as_mut().unwrap().next().expect("reached EOF")
                    };
                    x.parse().ok().expect("failed to parse")
                }
                None => {
                    self.iter = self.naive_read();
                    self.parse()
                }
            }
        }
    }
}