solution.py

# Due to another of his misbehaved, the primary school's teacher of the young Gauß, Herr J.G. Büttner,
# to keep the bored and unruly young schoolboy Karl Friedrich Gauss busy for a good long time,
# while he teaching arithmetic to his mates,
# assigned him the problem of adding up all the whole numbers from 1 through a given number n.

# Your task is to help the young Carl Friedrich to solve this problem as quickly as you can; so,
# he can astonish his teacher and rescue his recreation interval.

# Here's, an example:

# f(n=100) // returns 5050
# It's your duty to verify that n is a valid positive integer number.
# If not, please, return false (None for Python, null for C#).

# Note: the goal of this kata is to invite you to think about some 'basic' mathematic formula
# and how you can do performance optimization on your code.

# Advanced - experienced users should try to solve it in one line, without loops,
# or optimizing the code as much as they can.

# Credits: this kata was inspired by the farzher's kata 'Sum of large ints' .
# In fact, it can be seen as a sort of prep kata for that one.


def f(n):
    return None if not isinstance(n, int) or n <= 0 else n * (n + 1) // 2