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;

fn main() {
    let mut line = String::new();
    io::stdin().read_line(&mut line).unwrap();
    let nums: Vec<i32> =
        line.trim()
            .split_whitespace()
            .map(|x| x.parse().unwrap())
            .collect();
    let (mut a, b, _, mut k) = (nums[0], nums[1], nums[2], nums[3]);

    // takes A
    if k >= a {
        k -= a;
    } else {
        a = k;
        k = 0;
    }

    // takes B
    if k >= b {
        k -= b;
    } else {
        k = 0;
    }
    
    // takes C
    let c = -k;
    
    println!("{}", a + c);
}