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 <cmath>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <queue>
#include <map>
using namespace std;
const int MAXN = 30;
typedef long long LL;
const LL mod = 998244353;
int main()
{
    int n, k;
    scanf("%d %d",&n, &k);
    LL sum=0;
    if(k==0)
    {
        printf("%lld\n", 1LL*n*n);
        return 0;
    }
    for(int i=k+1;i<=n;++i)
    {
        sum+=n/i*(i-k);
        if(n%i!=0&&n%i>=k)
        {
            sum+=n%i-k+1;
        }
    }
    printf("%lld\n", sum);
    return 0;
}