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 n,k;
long long ans;
int main(){
	cin>>n>>k;
	for(int i=k+1;i<=n;i++){
		//cout<<i<<":";
		long long tmp=n/i;
		//cout<<tmp<<"---"<<(i-k)<<"  ";
		ans+=tmp*(i-k);
		tmp=n%i;
		tmp-=max(k-1,0);
		if(tmp>0) ans+=tmp;//cout<<tmp;
		//cout<<endl;
	}
	cout<<ans<<endl;
}