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
list($n, $k) = ints();
$ans = 0;
for ($b = $k + 1; $b <= $n; $b++) {
    $ans += intdiv($n, $b) * ($b - $k);
    $ans += max(0, $n % $b - $k + 1);
}
if ($k === 0) $ans -= $n - $k; // a=0の場合を除外
echo $ans;

function ints()
{
    return array_map('intval', explode(' ', trim(fgets(STDIN))));
}