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)

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

int main()
{
    long long n,k;
    scanf("%lld%lld",&n,&k);
    {
        long long sun=((n-k)+1)*(n-k)/2;
        for (int i=k+1;i<=n;i++)
        {
            for (int j=i-1;j>=1;j--)
            {
                if (i%j>=k) sun++;
            }
        }
        printf("%lld\n",sun);
    }
    return 0;
}