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 std::io::*;
use std::str::FromStr;

// 入力関数
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect(("failed to parse token"))
}

fn main() {
    let a:i32 = read();
    let b:i32 = read();
    let c:i32 = read();
    let k:i32 = read();

    let mut k_flag:i32 = 0;
    let mut counter:i32 = 0;
    for i in (0..a) {
        if k_flag == k {
            break
        }
        counter +=1;
        k_flag += 1;
    }

    for i in (0..b) {
        if k_flag == k {
            break
        }
        k_flag += 1;
    }

    for i in (0..c) {
        if k_flag == k {
            break
        }
        counter -= 1;
        k_flag += 1;
    }

    println!("{}", counter);
}