Byte on the stairs

During the 2018-2019 school year, a first-grader named Baytik occasionally arrived late for class. On one such day, while climbing the stairs, he invented a game: he would step onto the first step and then jump off, step onto the second step and jump off, and continue this pattern up to the n-th step. Baytik wondered how many steps he would take if he followed this game all the way to the n-th step.

Input

An integer n (n ≤ 10^9).

Output

A single number representing the total number of steps Baytik will take.

Examples