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: Accepted)

n,k = gets.split.map &:to_i

solve = -> b {
  q,r = (n + 1).divmod(b)
  ans = q * [b - k, 0].max
  ans += [r - k, 0].max
  k == 0 ? ans - 1 : ans
}

ans = 0
1.upto(n) do |i|
  ans += solve[i]
end

puts ans