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)

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

fn main() {
    let (a, b, c, k) = {
        let abck = get_line().split_whitespace()
            .map(|e| e.parse().unwrap())
            .collect::<Vec<i64>>();
        (abck[0], abck[1], abck[2], abck[3])
    };

    let mut sum = 0;

    if k < a {
        sum = k;
    } else {
        sum = a;

        let mut diff = k - a;
        if diff > 0 {
            diff -= b;
            if diff > 0 {
                sum -= diff;
            }
        }
    }
    println!("{}", sum);
}