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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.Scanner;

/**
 * B - Easy Linear Programming
 * 1 が書かれたカードが A 枚、0 が書かれたカードが B 枚、−1 が書かれたカードが C 枚あります。
 * これらのカードから、ちょうど K 枚を選んで取るとき、取ったカードに書かれた数の和として、 ありうる値の最大値はいくつですか。
 */
public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner( System.in );
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long k = sc.nextLong();

        long result = 0;


        if( k <= a ) {
            result = k;
        }
        else if( k <= a + b ) {
            result = a;
        }
        else if( k <= a + b + c ) {
            result = a - ( k - a - b );
        }

        System.out.println( result );

        sc.close();
    }
}