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: Time Limit Exceeded)

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#include <iostream>
#include <string>
#include <cstdio>
#include <vector>
#include <queue>
#include <list>
#include <cstdlib>
#include <algorithm>
#include <set>
#include <map>
#include <deque>
#include <cstring>
#include <cmath>
//#include<bits/stdc++.h>
using namespace std;

const int INF=0x3f3f3f3f;

int main(){
	int n,k_;
	scanf("%d%d",&n,&k_);
	long long ans=0;
	for(int k=k_;k<=n-1;k++) for(int i=k+1;i<=n;i++){
		ans+=(n-k)/i+(k!=0);
	}
	printf("%lld",ans);
	return 0;
}