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 (2.7.1) (judge verdict: Accepted)

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

def max(a,b); a > b ? a : b; end
def count_mod_ge_K(b)
  r,m = N.divmod(b)
  c = r * (b - K) + max(m + 1 - K, 0)
  K.zero? ? c - 1 : c
end
puts (K + 1 .. N).map{|b| count_mod_ge_K(b) }.sum