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