Translating pebbles

Sonya enjoys moving pebbles between piles. Initially, she has N piles, and sometimes she selects a pair of piles to transfer the smaller pile into the larger one. If the piles are equal in size, Sonya consults her brother to decide which pile to transfer. Your task is to help Sonya determine the maximum number of pebbles she might need to transfer in any given scenario.

Input

You are given a single number N (1 ≤ N ≤ 10000).

Output

Output a single number, which is the solution to the problem.

Examples