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 <stdlib.h>
#define int long long

int max(int a, int b){
	return a >= b ? a : b;
}

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