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: Time Limit Exceeded)

#include<stdio.h>
int main()
{
	int k,i,j;
	long long n,ans=0,t;
	scanf("%lld%d",&n,&k);
	if(k==0)
	{
		ans=n*n;
		printf("%lld\n",ans);
		return 0;
	}
	for(i=k;i<=n;i++)
	{
         ans=ans+n-i;
	}
    for(i=k+1;i<=n;i++)
    {
      for(j=1;j<=i-k;j++)
      {
    	t=(n-(k+j-1))/i;
       if(t>0) ans=ans+t;
      }
	}
	printf("%lld\n",ans);
	return 0;
}