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

namespace competitive_programming
{
    class Program
    {
        static void Main(string[] args)
        {
            var main = new Program();
            main.solve();
        }

        void solve()
        {
            int[] nk = Console.ReadLine().Split(' ').Select(val => int.Parse(val)).ToArray();
            int n = nk[0];
            int k = nk[1];

            int count = 0;
            for(int a = k != 0?k:1; a <= n; a++)
            {
                for(int b = k + 1; b <= n; b++)
                {
                    for (int x = 0; a - x * b >= k; x++)
                    {
                        long amari = a - x * b;
                        if (b > amari&&amari >= k)
                        {
                            count++;
                            //Console.WriteLine(a + " " + b + " " + (a - x * b));
                        }
                    }
                }
            }
            Console.WriteLine(count);
        }
    }
    struct Vector2
    {
        public Vector2(long x, long y)
        {
            this.x = x;
            this.y = y;
        }
        public long x;
        public long y;
    }

    struct Vector3
    {
        public int x;
        public int y;
        public int z;
    }
}