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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
	public class Main{
		public static void main(String[] args){
            Scanner sc = new Scanner(System.in);
            //入力
            long n = Integer.parseInt(sc.next());
            long k = Integer.parseInt(sc.next());
            long ret = 0;
            
            for(int i=(int)k+1; i<=n; i++){

            	ret += (n/i) * (i-k) + Math.max(0, n%i - Math.max(k, 1) + 1);
            	
            }
            
            System.out.println(ret);
            sc.close();
		}
    }