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: Time Limit Exceeded)

#include <iostream>
#include <cstdio>
using namespace std;
int main() {
    long long n, k;
    cin >> n >> k;
    if (k == 0) {
        cout << n * n << endl;
        return 0;
    }
    long long count = 0;
    for (int i = k; i <= n; i++) {
        count += n - i;
    }
    for (int i = k; i <= n; i++) {
        for (int j = k; j <= i; j++) {
            if (i % j >= k) {
                count++;
            }
        }
    }
    cout << count << endl;
}