import os

def main():
	a,b = map(int, input().split())
	if a <= b*2:
		print(0)
	else:
		print(a - b*2)


if __name__ == "__main__":
	main() import os os def main():
	a,b = map(int, input().split())
	if a <= b*2:
		print(0)
	else:
		print(a - b*2) main a,b = map(int, input().split()) a map(int, input().split()) map int input().split() ().split () input split b if a <= b*2:
		print(0)
	else:
		print(a - b*2) a <= b*2 a b*2 b 2 print(0) print 0 print(a - b*2) print a - b*2 a b*2 b 2 if __name__ == "__main__":
	main() __name__ == "__main__" __name__ "__main__" main() main def main():
	a,b = map(int, input().split())
	if a <= b*2:
		print(0)
	else:
		print(a - b*2) def main():
	a,b = map(int, input().split())
	if a <= b*2:
		print(0)
	else:
		print(a - b*2) main
import os

def main():
	a,b = map(int, input().split())
	if a <= b*2:
		print(0)
	else:
		print(a - b*2)


if __name__ == "__main__":
	main()
