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: Accepted)

<?php

$N = trim(fgets(STDIN));

$count = 0;
for ($a = 1; $a < $N; $a++) {
    for ($b = $a; $b < $N; $b++) {

        if ($a * $b >= $N) {
            break;
        }

        if ($a == $b) {
            $count += 1;
        } else {
            $count += 2;
        }
    }
}
echo $count;