Problem:
Score : 400 points

Problem Statement

Takahashi had a pair of two positive integers not exceeding N, (a,b), which he has forgotten.
He remembers that the remainder of a divided by b was greater than or equal to K.
Find the number of possible pairs that he may have had.

Constraints

1 \leq N \leq 10^5

0 \leq K \leq N-1

All input values are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the number of possible pairs that he may have had.

Sample Input 1

5 2

Sample Output 1

7

There are seven possible pairs: (2,3),(5,3),(2,4),(3,4),(2,5),(3,5) and (4,5).

Sample Input 2

10 0

Sample Output 2

100

Sample Input 3

31415 9265

Sample Output 3

287927211

Solution in PHP (5.6.30) (judge verdict: Accepted)

<?php
    $n;
    $k;
    $a = 0;
    fscanf(STDIN, "%d %d", $n, $k);
    for($i = $k + 1; $i <= $n; $i++){
        if($k == 0){
            $a--;
        }
        $x = floor(($n - $i + 1) / $i);
        $a += ($x + 1) * ($i - $k);
        $x++;
        if($x * $i + $k <= $n){
            $a += $n - $x * $i - $k + 1;
        }
        //echo "$a\n";
    }
    echo "$a\n";
?>