Multiplication Table

Find the middle element when the numbers in an n \times n multiplication table are sorted in increasing order. It is assumed that n is odd. For example, the 3 \times 3 multiplication table is as follows:

\begin{matrix} 1 & 2 & 3 \ 2 & 4 & 6 \ 3 & 6 & 9 \ \end{matrix}

The numbers in increasing order are [1,2,2,3,3,4,6,6,9], so the answer is 3.

Input

The only input line has an integer n.

Output

Print one integer: the answer to the task.

Constraints

1 \le n < 10^6

Example

Input

3

Output

3