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.Linq;
using static System.Console;
class K
{
	static void Main()
	{
		var I = ReadLine().Split().Select(long.Parse).ToArray();
		long N = I[0], K = I[1], sum = 0L;
		for (var b = K + 1; b <= N; b++)
		{
			var q = N % b;
			sum += (b - K) * (N / b);
			if (K <= q) sum += q - K + 1;
			if (K == 0) sum--;
		}
		WriteLine(sum);
	}
}