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;

int main() {
    int n, K;
    scanf("%d %d", &n, &K);
    if (!K) printf("%lld\n", 1LL * n * n), exit(0);
    long long ans = 0;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j += i) {
            int k = min(n, (j / i + 1) * i - 1);
            ans += max(0, k % i - K + 1);
        }
    }
    printf("%lld\n", ans);
    return 0;
}