Problem:
Score : 300 points

Problem Statement

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

Constraints

2 \leq N \leq 10^6

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

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

Solution in Python (3.8.2) (judge verdict: Accepted)

# -*- coding: utf-8 -*-

def input_int():
    return int(input())


def answer():
    n = input_int()

    count = 0
    for a in range(1, n):
        b = (n - 1) // a
        if b >= a:
            count += (b - a) * 2
            count += 1
        else:
            continue
    print(count)


answer()