Problem:
Score : 100 points

Problem Statement

The window of Takahashi's room has a width of A. There are two curtains hung over the window, each of which has a horizontal length of B. (Vertically, the curtains are long enough to cover the whole window.)

We will close the window so as to minimize the total horizontal length of the uncovered part of the window.
Find the total horizontal length of the uncovered parts of the window then.

Constraints

1 \leq A \leq 100

1 \leq B \leq 100

A and B are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

Print the total horizontal length of the uncovered parts of the window.

Sample Input 1

12 4

Sample Output 1

4

We have a window with a horizontal length of 12, and two curtains, each of length 4, that cover both ends of the window, for example. The uncovered part has a horizontal length of 4.

Sample Input 2

20 15

Sample Output 2

0

If the window is completely covered, print 0.

Sample Input 3

20 30

Sample Output 3

0

Each curtain may be longer than the window.

Solution in Java (OpenJDK 1.8.0) (judge verdict: Accepted)


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Scanner;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int k= 1;
        HashMap<String,Integer> hashMap = new HashMap<>();
        hashMap.put("SUN",7);
        hashMap.put("MON",6);
        hashMap.put("TUE",5);
        hashMap.put("WED",4);
        hashMap.put("THU",3);
        hashMap.put("FRI",2);
        hashMap.put("SAT",1);
        String s1;
        String s2;
        int a,b;
        while(k-->0){
            a=s.nextInt();
            b=s.nextInt();
            if((a-2*b)>0)
                System.out.println(a-2*b);
            else
                System.out.println(0);
        }
    }

    private static int binary_search(
            int arr[], int l,
            int h, int x)
    {
        while (l <= h) {
            int mid = (l + h) / 2;
            if (arr[mid] <= x)
                l = mid + 1;
            else
                h = mid - 1;
        }
        return h;
    }
    static int gcd(int a, int b)
    {
        if(b==0) {
            return a;
        }
        return gcd(b,a%b);
    }
    private static boolean isPrime(int n) {
        if (n == 2)
            return true;
        else if ((n % 2 == 0 && n > 2) || n < 2)
            return false;
        else {
            for (int i = 3; i <= (int) Math.sqrt(n); i += 2) {
                if (n % i == 0)
                    return false;
            }
            return true;
        }


    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

}