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 (7.4.4) (judge verdict: Accepted)

<?php
  list($n, $k) = explode(" ", trim(fgets(STDIN)));

  if($k == 0){
    echo $n*$n;
    exit;
  }
  $ans = 0;
  for($i=$k+1; $i<=$n; $i++){
    $round = intdiv($n, $i);
    $ans += $round * ($i-$k);
    $mod = $n % $i;
    if($mod >= $k){
      $ans += $mod - $k + 1;
    }
//    echo $ans.PHP_EOL;
  }

  echo $ans;