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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
fscanf(STDIN, "%d %d", $N, $K);
$ans = 0;
for ($i = $N; $i > 0; $i--) {
    $x = calc($N, $i, $K);
    $ans += $x;
}
printf("%d", $ans);

// $a 配る総数
// $b 配られる数
// $c 仕切り
function calc($a, $b, $c) {
    if ($c === 0) {
        return $a;
    } else {
        // 1つ当たり
        $d = intdiv($a, $b);
        // 余り
        $e = $a - $b * $d;
        $g = ($e >= $c) ? $e - $c + 1 : 0; 
        
        $f = $d * max(0, $b - $c);
        
        $h = $g + $f;
        //printf("a:%d b:%d c:%d d:%d amari:%d f:%d g:%d h:%d\n", $a, $b, $c, $d, $e, $f, $g, $h);
        return $h;
    }
}