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)

// -*- coding:utf-8-unix -*-

use proconio::input;

fn main() {
    input! {
        a: u64,
        b: u64,
        c: u64,
        k: u64,
    }

    // let mut ans = 0;
    // for i in 0..k {
    //     if a > 0 {
    //         ans += 1;
    //         a -= 1;
    //     } else if b > 0 {
    //         b -= 1;
    //     } else {
    //         ans -= k - i;
    //         break;
    //     }
    // }
    // println!("{}", ans);

    if k < a {
        println!("{}", k);
    } else if k < a + b {
        println!("{}", a);
    } else {
        println!("{}", a - (k - b - a));
    }
}