Sum of Natural Number in Python

# Python program to find the sum of natural numbers up to n where n is provided by user
# change this value for a different result
num = 16
# uncomment to take input from the user
#num = int(input("Enter a number: "))
if num < 0:

print("Enter a positive number")

else:

sum = 0
# use while loop to iterate un till zero
while(num > 0):

sum += num
num -= 1

print("The sum is",sum)

Output:

The sum is 136