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 int int64;

void run(void){
  int n,k;
  scanf("%d%d",&n,&k);
  if(k==0){
    printf("%lld\n",(int64)n*n);
    return;
  }
  int64 ans=0;
  for(int b=k+1;b<=n;b++){
    ans+=(int64)(n/b)*(b-k);
    if(n%b>=k){
      ans+=n%b-k+1;
    }
  }
  printf("%lld\n",ans);
}

int main(void){
  run();
  return 0;
}