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;
const int N=1e5+1;
int n,k;
long long ans;
int main(){
    ios::sync_with_stdio(false);
    cin>>n>>k;
    for (int i=k;i<=n;i++){
        int x=n-i;
        int j=i+1;
        while (j<=n){
            int l;
            if (x/j==0)l=n;
            else
                l=x/((x/j));
            ans+=(x/j)*(l-j+1);
            j=l+1;
        }
        if (i)ans+=n-i;
    }
    cout<<ans;
    return 0;
}