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
n=int(input())
count=0
for i in range(n-1):
  a=n-(i+1)
  b=math.sqrt(a)
  c=math.floor(b)
  cnty=0
  for j in range(c):
    if a%(j+1)==0:
      if j+1==b:
        cnty+=1
      else:
        cnty+=2
  count+=cnty
print(count)