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: Accepted)

from collections import Counter
N = int(input())
ans = 0
C = Counter([])
for a in range(1, N + 1):
    for b in range(1, N + 1):
        if a * b >= N:
            break
        ans += 1
        if a == b:
            C[a * b] += 1

for v in C.values():
    if v >= 2:
        ans -= (v - 1)
print(ans)