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: Wrong Answer)

fn main() {
    let (a, b, c, k) = read();
    let ans = solve(a, b, c, k);
    write(ans);
}

fn read() -> (u64, u64, u64, u64) {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let mut iter = s.split_whitespace();
    let a = iter.next().unwrap().parse::<u64>().unwrap();
    let b = iter.next().unwrap().parse::<u64>().unwrap();
    let c = iter.next().unwrap().parse::<u64>().unwrap();
    let k = iter.next().unwrap().parse::<u64>().unwrap();

    (a, b, c, k)
}

fn write(x: u64) {
    println!("{}", x);
}

fn solve(a: u64, b: u64, c: u64, k: u64) -> u64 {
    let mut r = k;
    let x = 
        if r >= a {
            a
        } else {
            r
        };
        r -= x;

        let y =
        if r >= b {
            b
        } else {
            r
        };
        r -= y;
    
        let z =
        if r >= c {
            c
        } else {
            r
        };
        //r -= z;
    
        x - z
}