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 <iostream>

using namespace std;

int main() {
  long long n = 0, k = 0;
  cin >> n >> k;
  if (k == 0) {
    cout << n * n << endl;
  } else {
    long long cnt = 0;
    for (long long i=k; i<=n; i++) {
      cnt += n-i;
      cnt += (n-i) / i * (i-k) + max(0ll, (n-i)%i - k + 1);
    }
    cout << cnt << endl;
  }
  return 0;
}