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: Wrong Answer)

<?php
    fscanf(STDIN, "%d", $N);
    $count = 0;
    
    // $i…与えられた数字を割る値
    for($C=1; $C < $N; $C++){
        // 余りが0の場合、$iは$numの約数となります
        for($A = 1; $A < $N - $C; $A++){
            if(($N - $C)%$A==0){
                $count++;
            }
        }
    }
    echo $C*$count;
?>