import sys


# input = sys.stdin.readline

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

if __name__ == "__main__":
    main() import sys sys def main():
    A,B = map(int,input().split())
    print(max(0,A-B*2)) main A,B = map(int,input().split()) A map(int,input().split()) map int input().split() ().split () input split B print(max(0,A-B*2)) print max(0,A-B*2) max 0 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())
    print(max(0,A-B*2)) def main():
    A,B = map(int,input().split())
    print(max(0,A-B*2)) main
import sys


# input = sys.stdin.readline

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

if __name__ == "__main__":
    main()