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)

def funcion_a(n):
  count = 0
  i = 2
  while i*i <= n:
    count += 1
    j = i + 1
    while i*j <= n:
      count += 2
      j += 1
    i += 1
  return count
  
n = int(input())
answer = funcion_a(n-1) + (n-2)*2 + 1
print(answer)