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 OCaml (4.10.0) (judge verdict: Accepted)

let rec kn a k = 
        if a <= 0 || k <= 0 then 
                0
        else if a < k then
                a
        else
                k


let () = Scanf.scanf "%d %d %d %d" (
fun a b c k -> 
        let an = kn a k in
        let bn = kn b (k - an) in
        let cn = kn c (k - an - bn) in
        an - cn
) |> Printf.printf "%d\n"