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.chomp.split(" ").map(&:to_i)

# a < b のとき
asb = (K..N-1).map { |a| N - a }.inject(:+)

# a >= b のとき
alb = 0
(K+1..N).each do |b|
  between = (N-b+1)
  slots = between / b
  rest = between % b
  alb += (b-K) * slots
  alb += rest - K if rest > K
  alb -= 1 if K == 0
end

puts alb + asb