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)

{-# OPTIONS_GHC -O2 -funbox-strict-fields #-}
import qualified Data.ByteString.Char8 as BC
import           Data.Maybe            (fromJust)

main :: IO ()
main = do
  [n, k] <- getInts
  print $ solve n k

solve :: Int -> Int -> Int
solve n k = sum $ map (countOverMod n k) [1 .. n]

countOverMod :: Int -> Int -> Int -> Int
countOverMod n 0 _ = n
countOverMod n k b = s * p + t where
  (p, q) = divMod n b
  s = max (b - k) 0
  t = max (q - k + 1) 0

readInts :: BC.ByteString -> [Int]
readInts = map (fst . fromJust . BC.readInt) . BC.words

getInts :: IO [Int]
getInts = readInts <$> BC.getLine