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 max(int a,int b){
  if(a > b){
    return a;
  }
  return b;
}

int main(void){
  int N,K;
  scanf("%d%d",&N,&K);

  long ans = 0;
  for(int b = K+1;b <= N;b++){
    int p = N/b;
    int r = N%b;
    ans += p*max(0,b-K)+max(0,r-K+1);
  }
  if(K == 0) ans -= N;

  printf("%ld\n",ans);
  return 0;
}