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 PyPy3 (7.3.0) (judge verdict: Time Limit Exceeded)

def N():
    return int(input())
def L():
    return list(map(int,input().split()))
def NL(n):
    return [list(map(int,input().split())) for i in range(n)]
mod = pow(10,9)+7
#import numpy
#import sympy
import math
def make_divisors(n):
    lower_divisors , upper_divisors = [], []
    i = 1
    while i*i <= n:
        if n % i == 0:
            lower_divisors.append(i)
            if i != n // i:
                upper_divisors.append(n//i)
        i += 1
    return lower_divisors + upper_divisors[::-1]
def divi(n):
    ans = {1}
    for i in range(2,int(n**0.5)+1):
        if n%i == 0:
            ans |= l[i]
            ans |= l[n//i]
    ans.add(n)
    return ans

n = N()
cnt = 1
l = [{} for _ in range(n)]
l[1] = {1}
for i in range(2,n):
    #l[i] = make_divisors(i)
    l[i] = divi(i)
    cnt += len(l[i])

print(cnt)