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 n, k, ans=0;

// n=xの組の数を求める
void f(int n, int k){

  // a<b : (n-k)+(n-k-1)+...+2+1
  ans += n-k;

  // a>b : a<n, a%b>=k
  for(int i=1; i<n; i++){
    if(n%i>=k){
      ans++;
    }
  }

  if(n>k){
    f(n-1, k);
  }
}



int main(){
  
  scanf("%d\t%d", &n, &k);
  
  f(n, k);

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

  return 0;
}