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 Python (3.4.3) (judge verdict: Wrong Answer)

# a%b >= K iff xb+K <= a < (x+1)b
# bごとに数えるだけ

N,K = map(int,input().split())
ans = 0

for b in range(K+1,N+1):
  cnt = 0
  x_max = N//b
  # 0 <= x < x_max
  # 各xに対してb-K個ある
  cnt += x_max * (b-K)
  # x = x_max
  lower = x_max*b+K
  if lower <= N:
    upper = min((x_max+1)*b-1,N)
    cnt += upper - lower + 1
  ans += cnt
  
print(ans)