Problem:
Score : 300 points

Problem Statement

Given is a positive integer N.
How many tuples (A,B,C) of positive integers satisfy A \times B + C = N?

Constraints

2 \leq N \leq 10^6

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

3

Sample Output 1

3

There are 3 tuples of integers that satisfy A \times B + C = 3: (A, B, C) = (1, 1, 2), (1, 2, 1), (2, 1, 1).

Sample Input 2

100

Sample Output 2

473

Sample Input 3

1000000

Sample Output 3

13969985

Solution in C# (Mono-csc 3.5.0) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Globalization;
using System.Linq;
using System.Text;

class Program
{


    static void Main(string[] args)
	{
        int N = int.Parse(Console.ReadLine());

        int A = 1;

        int count = 0;

        for (int i = 0; i < N; i++)
        {
            int B = 1;

            for(int j = 0;j < N; j++)
            {

                if(A * B < N)
                {
                    count++;
                    B++;
                }
                else
                {
                    break;
                }
            }

            A++;
        }


        Console.WriteLine(count);
    }
}