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 C++14 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <cstdio>
using namespace std;
int main() {
    int n, k;
    scanf("%d%d", &n, &k);
    int res = 0;
    for (int b = k+1; b <= n; b++) {
        int div = n / b;
        int pad = n % b;
        res += div * (b - k);   // 余りがk以上はb-k個ずつ
        if (k == 0) res += pad;
        else if (pad >= k) res += (pad - k + 1);
    }
    printf("%d\n", res);
}