#!/usr/bin/python3

def main():
  n, k = map(int, input().split(' '))
  if k == 1:
    print(0)
    return

  print(n - k)
  return

if __name__ == '__main__':
  main() def main():
  n, k = map(int, input().split(' '))
  if k == 1:
    print(0)
    return

  print(n - k)
  return main n, k = map(int, input().split(' ')) n map(int, input().split(' ')) map int input().split(' ') ().split () input split ' ' k if k == 1:
    print(0)
    return

   k == 1 k 1 print(0) print 0 return print(n - k) print n - k n k return if __name__ == '__main__':
  main() __name__ == '__main__' __name__ '__main__' main() main def main():
  n, k = map(int, input().split(' '))
  if k == 1:
    print(0)
    return

  print(n - k)
  return def main():
  n, k = map(int, input().split(' '))
  if k == 1:
    print(0)
    return

  print(n - k)
  return main
#!/usr/bin/python3

def main():
  n, k = map(int, input().split(' '))
  if k == 1:
    print(0)
    return

  print(n - k)
  return

if __name__ == '__main__':
  main()