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# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
using E = System.Linq.Enumerable;

class Program
{
    static void Main(string[] args)
    {
        //入力を受け取る
        var NK = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
        var N = NK[0];
        var K = NK[1];
      
        var ans = 0L;
      
      　//割る数を固定する
        for(int i = 1;i <= N ;i++){
          //iの倍数ごとのK以上の余りの数
          ans += (N/i)*Math.Max(i-K,0);
          ans += Math.Max((N%i)-K+1,0);
        }
        Console.WriteLine(ans);
    }
}