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

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

main()
