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


if __name__ == "__main__":
    main() def main():
    A, B = map(int, input().split())
    if A < B * 2:
        print(0)
        exit(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)
        exit(0)
    else:
        print(A - B * 2) A < B * 2 A B * 2 B 2 print(0) print 0 exit(0) exit 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)
        exit(0)
    else:
        print(A - B * 2) def main():
    A, B = map(int, input().split())
    if A < B * 2:
        print(0)
        exit(0)
    else:
        print(A - B * 2) main
def main():
    A, B = map(int, input().split())
    if A < B * 2:
        print(0)
        exit(0)
    else:
        print(A - B * 2)


if __name__ == "__main__":
    main()
