Sum 3

Find the sum of all odd natural numbers up to a given odd number $n$. Do not use loops.

Note: To solve without loops, use the formula for the sum of odd numbers: $1 + 3 + 5 + \dots + (2k-1) = k^2$, where $k = \frac{n+1}{2}$.

A single line contains an odd natural number $n$.

Print a single integer — the sum of all odd natural numbers up to $n$.

• $1 \le n \le 10^9$
• $n$ is odd