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: Time Limit Exceeded)

#include <stdio.h>

int main(){
  long n, k, ans=0;

  scanf("%ld\t%ld", &n, &k);

  // a<b : (n-k)+(n-k-1)+...+2+1
  for(int i=1; i<=n-k; i++){
    ans += i;
  }
  //printf("%ld\n", ans);

  // a>b : a>3, b>=k+1>=2, bはaの約数でない
  for(int i=k+2; i<=n; i++){
    for(int j=k+1; j<i; j++){
      if(i%j>=k){
	ans++;
      }
      //printf("%d,%d\n", i, j);
    }
  }

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

  return 0;
}