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 proconio::input;

fn main() {
    input! {
        a: i32,
        b: i32,
        _c: i32,
        k: i32,
    }

    solve(a, b, k);
}

fn solve(a: i32, b: i32, k: i32) {
    // a が十分多いとき
    if a >= k {
        println!("{}", k);
        return;
    }

    // a と b で十分多いとき
    if a + b >= k {
        println!("{}", a);
        return;
    }

    // c まで使わないといけないとき
    println!("{}", a - (k - a - b));
}