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: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var nk = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            int count = 0;
            for (int b = 1; b < nk[0]; b++)
            {
                for (int a = b + 1; a <= nk[0]; a++)
                {
                    if (a % b >= nk[1]) count++;
                }
            }
            for(int i = nk[1]; i < nk[0];i++)
            {
                count = count + nk[0] - i;
            }
            Console.WriteLine(count);
        }
    }
}