import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10 ** 9)
INF = 1 << 60
MOD = 1000000007


def main():
    A, B = map(int, readline().split())
    
    print(max(0, A - 2 * B))
    
    return


if __name__ == '__main__':
    main() import sys sys read = sys.stdin.read read sys.stdin.read sys.stdin sys stdin read readline = sys.stdin.readline readline sys.stdin.readline sys.stdin sys stdin readline readlines = sys.stdin.readlines readlines sys.stdin.readlines sys.stdin sys stdin readlines sys.setrecursionlimit(10 ** 9) sys.setrecursionlimit sys setrecursionlimit 10 ** 9 10 9 INF = 1 << 60 INF 1 << 60 1 60 MOD = 1000000007 MOD 1000000007 def main():
    A, B = map(int, readline().split())
    
    print(max(0, A - 2 * B))
    
    return main A, B = map(int, readline().split()) A map(int, readline().split()) map int readline().split() ().split () readline split B print(max(0, A - 2 * B)) print max(0, A - 2 * B) max 0 A - 2 * B A 2 * B 2 B return if __name__ == '__main__':
    main() __name__ == '__main__' __name__ '__main__' main() main INF = 1 << 60 1 << 60 INF readlines = sys.stdin.readlines sys.stdin.readlines readlines readline = sys.stdin.readline sys.stdin.readline readline read = sys.stdin.read sys.stdin.read read def main():
    A, B = map(int, readline().split())
    
    print(max(0, A - 2 * B))
    
    return def main():
    A, B = map(int, readline().split())
    
    print(max(0, A - 2 * B))
    
    return main MOD = 1000000007 1000000007 MOD
import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10 ** 9)
INF = 1 << 60
MOD = 1000000007


def main():
    A, B = map(int, readline().split())
    
    print(max(0, A - 2 * B))
    
    return


if __name__ == '__main__':
    main()
