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

-----Sample Input-----
4

-----Sample Output-----
23

We have f(1)=1, f(2)=2, f(3)=2, and f(4)=3, so the answer is $1\times 1 + 2\times 2 + 3\times 2 + 4\times 3 =23$.

见题面

见题面