Write a Python Program to Calculate sum of N natural number. N should be taken from the keyboard

# Sum of natural numbers up to num
N = float(input('enter natural number: '))

if N < 0:
   print("this number is not natural, natural number should be a positive number")
else:
   sum = 0
   # use while loop to iterate until zero
   while(N > 0):
       sum += N #same as sum=sum+N
       N -= 1
   print("The sum is", sum)