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)

def d_remainder_reminder(N, K):
    ans = 0
    for b in range(K + 1, N + 1):
        # N=pb+r(0<=r<b) と表すと、aを"0"からNまで変化させたときに
        # a%bを順に並べた列は、[0,1,2,...,b-1]*p + [0,1,2,...,r] となる
        p = N // b
        r = N % b
        # 条件を満たすaの個数は、p*max(0,b-K) + max(0,r+1-K) 個
        ans += p * max(0, b - K) + max(0, r + 1 - K)
    if K == 0:
        # K=0のとき、1回のループで1だけ解が大きくなる(a=0の分を足してしまうため)
        # その分を差し引く
        ans -= N
    return ans