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)

#![allow(non_snake_case)]
use proconio::input;
// use std::collections::HashMap;

fn main() {
    input! {
        A: i64,
        B: i64,
        _C:i64,
        K:i64,
    }

    let mut ans = 0;
    let mut rest = K;
    // Aを使いきって終わり
    if rest <= A {
        ans += rest;
        println!("{}", ans);
        return;
    }

    rest -= A;
    ans += A;

    // Bを使いきって終わり
    if rest <= B {
        println!("{}", ans);
        return;
    }

    rest -= B;

    // やむを得ずCを使う
    ans -= rest;

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