# Compute n-factorial using a function.

#
#  Compute the factorial of a number
# 
#  Parameters:
#    n: An integer for which the factorial is being computed.  Returns
#       1 if n is a negative number.
#
#  Returns:
#    n-factorial
#
def factorial(n):
  result = 1
  for i in range(1, n+1):
    result = result * i

  return result

#
#  Compute n-factorial for a number entered by the user.
#
#  Parameters: (None)
#
#  Returns: (None)
#
def main():
  a = int(input("Enter a non-negative integer: "))
  print(a, "factorial is", factorial(a))

# Start the main function
main()