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>
#include<cstdio>
#include<cstring>
using namespace std;
long long ans,n,k;
long long maxx(long long a,long long b)
{
	if(a>b)  return a;
	else     return b;
}
int main()
{
	cin>>n>>k;
	n++;
	for(long long i=k+1;i<n;i++)//1---n-1
	{
		long long x=i-k;
		ans+=n/i*x+maxx(0,n-n/i*i-k);
	} 
	printf("%lld\n",ans-(!k)*(n-1));
	return 0;
}