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Contest: Task: Related: TaskC TaskE

Score : 400 points

Problem Statement

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

Given a positive integer N, find NK=1K×f(K).

Constraints

  • 1N107

Input

Input is given from Standard Input in the following format:

N

Output

Print the value NK=1K×f(K).


Sample Input 1

4

Sample Output 1

23

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


Sample Input 2

100

Sample Output 2

26879

Sample Input 3

10000000

Sample Output 3

838627288460105

Watch out for overflows.

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