Sum of natural numbers

Write a function sum_natural_numbers that takes a positive integer n and returns the sum of all natural numbers from 1 to n.
def sum_natural_numbers(n):
# complete function here...
print(sum_natural_numbers(5)) # expected output: 15 print(sum_natural_numbers(7)) # expected output: 28 print(sum_natural_numbers(77)) # expected output: 3003
Python
Setting up Python environment...
Output