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 Ruby (2.3.3) (judge verdict: Wrong Answer)

N, K = gets.split.map(&:to_i)

def count(range)
  if range.begin > range.end 
    return 0
  end
  (range.end - range.begin + 1)
end

ans = 0
for b in (K+1)..N
  n_chunks = N / b 
  x = n_chunks * count(K..(b-1))
  ans += x
  rest = N % b
  y = count(K..rest)
  ans += y
  #p b: b, n_chunks: n_chunks, x: x, rest: rest, y: y
end
p ans