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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using static System.Math;
using static System.Array;


namespace AtCoder
{
    class AC
    {
        const int mod = 1000000007;
        const int INF = int.MaxValue / 2;
        const long SINF = long.MaxValue / 2;


        static void Main(string[] args)
        {
            //var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            //Console.SetOut(sw);
            var cin = new Scanner();

            var p = cin.SplitReader();
            int N = p[0];
            int K = p[1];
            long ans = 0;
            for(var b = K + 1; b <= N; b++)
            {
                int M = (N - K) / b;
                ans += M * (b - K);
                
                int L = N % b;
                ans += L >= K ? L - K + 1 : b - K;
                if (K == 0) { ans--; }
            }

            Console.WriteLine(ans);

            //Console.Out.Flush();
        }

        

    }
    public class Scanner
    {
        public int[] SplitReader()
        {
            int[] array = Console.ReadLine().Split().Select(int.Parse).ToArray();
            return array;
        }
        public long[] SplitReaderL()
        {
            long[] array = Console.ReadLine().Split().Select(long.Parse).ToArray();
            return array;
        }
    }

   public static class Tool
        {
            static public void Initialize<T>(ref T[] array, T initialvalue)
            {
                for (var i = 0; i < array.Length; i++)
                {
                    array[i] = initialvalue;
                }
            }
            static public long ModuloP(long value, long mod)
            {
                long r = value % mod;

                if (r * mod < 0)
                {
                    r += mod;
                }
                return r;
            }

        }

   struct Pair<T> : IComparable<Pair<T>> where T : IComparable<T>
   {
        public T variable;
        public int index;

        public Pair(T val, int i)
        {
            variable = val;
            index = i;
        }

        public int CompareTo(Pair<T> otherPair)
        {
            return variable.CompareTo(otherPair.variable);
        }

        public int CompareIndex(Pair<T> otherPair)
        {
            return index.CompareTo(otherPair.index);
        }
   }

    


}