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: Wrong Answer)

#include<stdio.h>
int main(void) {
	unsigned long n, k, i, j, h;
	unsigned long cont = 0;
	scanf("%lu%lu", &n, &k);
	cont += 0.5 * (n - k) * (n - k + 1);
	for (i = 1; i <= n; i++) {
		if (i % 2) {
			cont += (i + 1) / 2 - k;
			for (j = 1; j <= (i + 1) / 2 - k + 1; j++) {
				if (i % j >= k)cont += 1;
			}
		}
		else {
			cont += (i + 2) / 2 - k;
			for (j = 1; j <= (i + 2) / 2 - k + 1; j++) {
				if (i % j >= k)cont += 1;
			}
		}
	}
printf("%lu", cont);
return 0;
}