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: Time Limit Exceeded)

import math
def num_divisors_trial_division(n):
    num = 0
    for i in range(1, int(math.sqrt(n) + 1e-9) + 1):
        if n % i == 0:
            num += 1
            if n != i**2:
                num += 1
    
    return num
n = int(input())
ans = 0
for i in range(1,n):
    ans += num_divisors_trial_division(i)
print(ans)