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: Wrong Answer)

import math
N=int(input())

def era(n):
  prime=[]
  furui=list(range(2,n+1))
  while furui[0]<math.sqrt(n):
    prime.append(furui[0])
    furui=[i for i in furui if i%furui[0]!=0]
  return prime+furui

furui=era(10**6+7)
minfac=list(range(10**6+7))
for i in furui:
  for j in range(i,(10**6+7)//i):
    if minfac[i*j]==i*j:
      minfac[i*j]=i
ans=0   
for i in range(1,N):
  temp=1
  temp2=1
  l=minfac[i]
  while i != 1:
    if l!=minfac[i]:
      temp*=temp2
      temp2=2
    else:
      temp2+=1
    l=minfac[i]
    i=i//l
  temp*=temp2
  ans+=temp
print(ans)