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)

def yaku(k):
    count  = 0
    an = []
    for i in range(1,k+1):
        if len(an) > 0 and i == an[-1]:
            count += len(an)
            break
        if k % i == 0:
            count += 1
            if k/i != i:
                an.append(k/i)
    return count

n = int(input())
ans = 0
for i in range(n-1):
    count = yaku(n-i-1)
    ans += count
print(ans)