Sum of the First N Natural Numbers

Given a non-negative integer n, return the sum of the first n natural numbers, starting from 1.

The required sum is 1 + 2 + ... + n. When n = 0, there are no terms to add, so return 0.

You may use a loop or the arithmetic formula n * (n + 1) / 2. The result is guaranteed to fit within a signed 64-bit integer.

Examples:

• n = 5 returns 15.
• n = 1 returns 1.
• n = 0 returns 0.

Implement sumNaturalNumbers(n).

0 <= n <= 100000000 The result fits within a signed 64-bit integer and within the safe integer range used by the importer.