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.math.BigInteger;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Main {

	static final boolean debugMode = false;

	static final long DIV_INF = 1000000007l;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long a = readLong(sc);
		long b = readLong(sc);
		long c = readLong(sc);
		long k = readLong(sc);

		if (k <= a) {
			System.out.println(k);
			return;
		} else if (k <= a + b) {
			System.out.println(a);
		} else {
			System.out.println(a - (k - a - b));
		}

	}

	static int readInt(Scanner sc) {
		return Integer.parseInt(sc.next());
	}

	static Long readLong(Scanner sc) {
		return Long.parseLong(sc.next());
	}

	static void log(String s) {
		if (debugMode) {
			System.out.println(s);
		}
		return;
	}
}

class KrmlUtil {
	// a >= b
	static int gcd(int a, int b) {
		while (true) {
			if (b == 0)
				break;

			int mod = a % b;
			a = b;
			b = mod;
		}
		return a;
	}

	// a >= b
	static int lcm(int a, int b) {
		return a * b / gcd(a, b);
	}

	// a >= b
	static long gcd(long a, long b) {
		while (true) {
			if (b == 0)
				break;

			long mod = a % b;
			a = b;
			b = mod;
		}
		return a;
	}

	// a >= b
	static long lcm(long a, long b) {
		return a * b / gcd(a, b);
	}

	static BigInteger gcd(BigInteger a, BigInteger b) {
		return a.gcd(b);
	}

	static BigInteger lcm(BigInteger a, BigInteger b) {
		return a.divide(a.gcd(b)).multiply(b);
	}
}

class Pair {
	private int x;
	private int y;

	public int getX() {
		return x;
	}

	public void setX(int x) {
		this.x = x;
	}

	public int getY() {
		return y;
	}

	public void setY(int y) {
		this.y = y;
	}

	public Pair() {

	}

	public Pair(int x, int y) {
		this.x = x;
		this.y = y;
	}

}