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: Time Limit Exceeded)

n, k = gets.chomp.split(" ").map(&:to_i)
a = Array.new(n+1)
a[0] = 0

def countNumber(a, b)
  count = 0
  for i in (b+1)..a do
    if a % i >= b
      count += 1
    end
  end
  return count
end

for i in 1..n do
  a[i] = a[i-1] + countNumber(i, k)
  if i - k > 0
    if k == 0
      a[i] += (i -k) - 1
    else
      a[i] += (i -k)
    end
  end
end

p a[n]