Problem Statement

Given is a positive integer N.
How many tuples (A,B,C) of positive integers satisfy $A \times B + C = N$?

Input

Input is given from Standard Input in the following format:
N

Output

Print the answer.

Constraints

• $2 \leq N \leq 10^6$
• All values in input are integers.

Sample Input 1

3

Sample Output 1

3

There are 3 tuples of integers that satisfy $A \times B + C = 3$: (A, B, C) = (1, 1, 2), (1, 2, 1), (2, 1, 1).

Sample Input 2

100

Sample Output 2

473

Sample Input 3

1000000

Sample Output 3

13969985

见题面 Input 部分

见题面 Output 部分