# from http://www.senktec.com/2013/09/one-way-to-do-it/

def f1(n):
  if n > 1:
    return n * f1(n - 1)
  else:
    return 1

def f2(n):
  return n * f2(n - 1) if n > 1 else 1

def f3(n):
  if n <= 1: return 1
  else: return f3(n - 1) * n 

def f4(n, accumulator=1):
  if n == 0:
    return accumulator
  else:
    return f4(n - 1, accumulator * n)

f5 = lambda n: n and n * f5(n - 1) or 1

def f6(n):
  result = 1
  for i in range(1, n + 1):
    result *= i 
  return result

def f7(n): 
  result = 1 
  while n > 0:
    result *= n
    n -= 1
  return result

def f8(n):
  if n == 0:
    return 1
  else:
    return reduce(lambda a,b: a * b, range(1, n + 1))

def f9(n):
  numbers = xrange(1, n + 1)
  if len(numbers) == 0:
    return 1
  return reduce(int.__mul__, numbers)

def f10(n):
  if n == 0: return 1
  return eval('*'.join([str(i) for i in range(1, n + 1)]))