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)

#473 A*B+C=Nの組み合わせ .. A*B=N-C
import math
count=0
N=int(input())
for C in range(1,N):
  for AorB in range(1,int(math.sqrt(N-C))+1):
    if (N-C) % AorB==0:
      if AorB==math.sqrt(N-C):
      	count+=1
      else:
      	count+=2
print(count)