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;
using ll=long long;
#define MAX 5000
#define MOD 1000000007

int main(){
  ll N,K;
  cin>>N>>K;
  ll ans=0;
  if(K==0){
    cout<<N*N<<endl;
  }else{
    for(ll b=K+1;b<=N;b++){
      ll x=N/b;
      ans+=x*(b-K);
      ans+=max<ll>(0,N-b*x-K+1);
    }
    cout<<ans<<endl;
  }
}