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 PHP (7.4.4) (judge verdict: Time Limit Exceeded)

<?php

$n = trim(fgets(STDIN));

$count = 0;

for($i=1; $i<$n; $i++){
    $s = $n - $i;
    for($j=1; $j<=$s; $j++) {
        if($s % $j == 0) {
            $count++;
        } else {
            continue;
        }
    }
}

echo $count;