#
#  Compute n-factorial using a function.
#

# Compute the value of n-factorial.
def factorial(n):
  # Initialize result.
  result = 1

  # Multiply result by 1, 2, 3 ... n-2, n-1, n
  for factor in range(1, n + 1):
    result = result * factor

  # Return the result.
  return result


# Read an integer from the user, compute its factorial, and display the result.
def main():
  n = int(input("Enter a non-negative integer: "))

  r = factorial(n)

  print(f"{n} factorial is equal to {r}.")

# Call the main function.
main()