# Lesson 2 Task 4: get number factorial
# Author: Stanislav Mykhailenko
# License: Unlicense
try:
number = int(input("Enter a natural number: "))
if number < 1:
raise ValueError("A natural number is required.")
factorial = 1
for nextNumber in range(2, number + 1):
factorial = factorial * nextNumber
print(str(number) + " factorial is " + str(factorial))
except ValueError:
print("Invalid number entered.")
