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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
int main(void)
{
    long int n,k;
    scanf("%ld %ld",&n,&k);
    long long int ans=0;
    if(k==0)
    {
        ans=n*n;
        printf("%lld",ans);
        return 0;
    }
    if(k>=n)
    {
        printf("0");
        return 0;
    }
    ans+=(n-k)*(n-k+1)/2;
    for(int p=k+1;p<n;p++)
    {
        ans+=(p-k)*(n/p-1);
        if(n%p>k-1)ans+=n%p-k+1;
    }
    printf("%lld",ans);
}