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