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: Wrong Answer)

use std::io;

fn main() {
	let mut buf = String::new();
	io::stdin().read_line(&mut buf).expect("");
	let mut iter = buf.split_whitespace();
	let a:u64 = match iter.next().unwrap().parse() {
		Ok(n) => n,
		Err(_) => panic!(""),
	};
	let b:u64 = match iter.next().unwrap().parse() {
		Ok(n) => n,
		Err(_) => panic!(""),
	};
	let c:u64 = match iter.next().unwrap().parse() {
		Ok(n) => n,
		Err(_) => panic!(""),
	};
	let k:u64 = match iter.next().unwrap().parse() {
		Ok(n) => n,
		Err(_) => panic!(""),
	};
	let mut flag = true;
	if a >= k {
		println!("{}", k);
	}else if a + b >= k {
		println!("{}", a);
	}else{
		for num in 1..(c+1) {
			 if a + b + num == k {
			 	flag = false;
			 	println!("{}", a - num);
			 }
		}
	}
}