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)

if k==0
  puts n*n
  exit 0
end

ret=0
((k+1)..n).each do |b|
  if n-b+1<b
    ret+=[(n-b+1)-k, 0].max
  else
    m=n-b+1
    ret+=m/b*(b-k)
    l=m/b*b
    ret+=[m-l-k, 0].max 
  end
end

puts ret+(n-k)*(n-k+1)/2