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 abc090d
{
    class Program
    {
        static void Main(string[] args)
        {
            var buf = Console.ReadLine().Split();
            var n = int.Parse(buf[0]);
            var k = int.Parse(buf[1]);
            var ans = 0;

            for (var b = k + 1; b <= n; ++b) {
                for (var a = b + k; a <= n; ++a) {
                    if (a % b >= k) ++ans;
                }
            }
            ans += (n - k + 1) * (n - k)>>1;

            Console.WriteLine(ans);
        }
    }
}