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 test
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
            var N = input[0];
            var K = input[1];
            var ans = 0;
            for(var i = 1; i <= N; i++)
            {
                var p = N / i;
                var r = N % i;
                if (K > 0)
                {
                    ans += Math.Max(0, p * Math.Max(0, i - K)) + Math.Max(0, r - K + 1);
                }
                else
                {
                    ans += p * i + r;
                }
            }

            Console.WriteLine(ans);
        }
    }
}