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 read_vec<T: std::str::FromStr> () -> Vec<T> {
  let mut s = String::new();
  std::io::stdin().read_line(&mut s).ok();
  s.trim().split_whitespace().map(|x| x.parse().ok().unwrap()).collect()
}

fn main(){
  let mut data: Vec<i32> = read_vec();
  let mut k = data.pop().unwrap();
  let mut out = 0;
  for (i, val) in data.into_iter().enumerate(){
    if k - val < 0{
      out += (1 - i as i32) * k;
      break
    }
    out += (1 - i as i32) * val;
    k -= val;
  }
  println!("{}", out);
}