Factorial of a number.

num = int(input("Enter a number: "))  
factorial = 1  
if num < 0:  
   print("Sorry, factorial does not exist for negative numbers")  
elif num == 0:  
   print("The factorial of 0 is 1")  
else:  
   for i in range(1,num + 1):  
       factorial = factorial*i  
   print("The factorial of",num,"is",factorial)