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: Wrong Answer)

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

#define ll long long
#define INF 10e10
#define rep(i,n) for(int i=0; i<n; i++)
#define repr(i,n,m) for(int i=m; i<n; i++)
#define MAX 100
#define MOD 1000000007
#define pb push_back
#define debug(x) cout << x << endl;
#define END cout << endl;
#define sorti(x) sort(x.begin(), x.end())

int main() {
  int n,k; cin >> n >> k;
  ll res = 0;

  if (k == 0) {
    cout << pow(n,2) << endl;
    return 0;
  }

  for (int i = k+1; i < n; ++i) {
    int num = i - k;
    int cnt = floor((double) n / i);
    res += cnt * num;

    int pos = k + (i * cnt);
    if (pos <= n) {
      res += n - pos + 1;
    }
  }

  cout << res << endl;
}