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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Debug.Trace
import Data.List

main :: IO ()
main = do
  [n, k] <- (map read . words) <$> getLine :: IO [Int]
  print $ sum $ map (\b -> (subtotal n k b)) [k + 1 .. n]

subtotal n k b =
  let low = (n - (b - 1)) `div` b
      high = (n - k) `div` b
      d = if k == 0 then 1 else 0
  in
    if low < high
      then
        let m = low * b + b
        in
          (low + 1) * (m - (n - (b - 1))) + (high + 1) * (n - k - m + 1) - d
      else (low + 1) * (b - k) - d