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