Problem Statement

For a positive integer $X$, let $f(X)$ be the number of positive divisors of $X$.

Given a positive integer $N$, find $\sum_{K=1}^N K\times f(K)$.

Constraints

• $1 \leq N \leq 10^7$

Input

Input is given from Standard Input in the following format:

N

Output

Print the value $\sum_{K=1}^N K\times f(K)$.