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

namespace ABC_D
{
    class D090
    {
        static void Main(string[] args)
        {
            int[] h = Console.ReadLine().Split(' ').Select(z => int.Parse(z)).ToArray();
            int N = h[0], K = h[1];

            long counter = 0;
            for (int i = K + 1; i <= N; i++)
            {
                int turn = N / i;
                long q = (long)turn * (i - K);
                int p = K == 0 ? 0 : Math.Max(0, N % i - K + 1);
                counter += (q + p);
            }
            Console.WriteLine(counter);
        }

    }
}