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 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;

#define repeat(i, x) for (int64_t i = 0; (i) < (int64_t)(x); (i)++)

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int64_t n, k;
    cin >> n >> k;

    if (k == 0) {
        cout << n * n << endl;
        return 0;
    }

    int64_t ans = 0;
    for (int64_t b = 1; b <= n; b++) {
        ans += (n / b) * max(b - k, (int64_t)0);

        if (k > 0) {
            ans += max((n % b + 1) - k, (int64_t)0);
        }
        // cerr << "b: " << b << " cnt: " << (n / b) * max(b - k, 0) + max(n % b - k, 0) << endl;
    }

    cout << ans << endl;

    return 0;
}