AT_abc449_a [ABC449A] π

You are given a positive integer $ D $ . Find the area of a circle with diameter $ D $ .

The input is given from Standard Input in the following format: > $ D $

Output the answer. Your answer is considered correct if the absolute or relative error from the true answer is at most $ 10^{-6} $ .

### Sample Explanation 1 The area of a circle with diameter $ 2 $ is $ 3.141592653589793\ldots $ . ### Constraints - $ 1\le D\le 100 $ - The input value is an integer.