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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;

int main(){
  int K,N;
  cin >> N >> K;

  if(N==1){
    cout << 1 << endl;
  }else{
    int count=0,i,b;
    for(i=K; i<N/2.0; i++){
      if(i==0){
        for(b=1; b<=N/2; b++){
          count += N/b;
        }
        count += ((N%2==0)? N/2 : N/2+1);
        continue;
      }
      for(b=i+1; b<=N-i; b++){
        count += (N-i)/b+1;
      }
      count += i;
    }
    count += (N/2)*(N/2+1)/2;
    cout << count <<endl;
  }
}