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>
#include <inttypes.h>

int main(void) {
	int N, K;
	int b;
	uint64_t answer = 0;
	if (scanf("%d%d", &N, &K) != 2) return 1;
	for (b = K + 1; b <= N; b++) {
		int kazu = N + 1;
		int blockCount = (kazu + b - 1) / b;
		int saigo = N % b;
		/* uint64_t bak = answer; */
		answer += blockCount * (b - K);
		if (saigo >= K) answer -= b - (saigo + 1); else answer -= b - K;
		if (K == 0) answer--;
		/* printf("debug %d %d\n", b, (int)(answer - bak)); */
	}
	printf("%" SCNu64 "\n", answer);
	return 0;
}