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>

typedef long long ll;

int main() {

	ll N,K;

	scanf("%lld %lld",&N,&K);

	ll i;

	ll ans=0ll;

	for(i=K+1ll;i<=N;i+=1ll){
	ll r=N%i;
	ll p=N/i;
	if(i-K>0ll){ans+=p*(i-K);}
	if(r-K+1ll>0){ans+=r-K+1ll;}
	}

	if(K==0ll){ans=N*N;}

	printf("%lld\n",ans);

	return 0;
}