import sys
input = lambda: sys.stdin.readline().rstrip()

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

if __name__ == '__main__':
    main() import sys sys input = lambda: sys.stdin.readline().rstrip() input lambda: sys.stdin.readline().rstrip() sys.stdin.readline().rstrip() sys.stdin.readline().rstrip sys.stdin.readline() sys.stdin.readline sys.stdin sys stdin readline rstrip 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 input = lambda: sys.stdin.readline().rstrip() lambda: sys.stdin.readline().rstrip() input 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 sys
input = lambda: sys.stdin.readline().rstrip()

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

if __name__ == '__main__':
    main()