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-mcs 6.8.0.105) (judge verdict: Accepted)

using System;
using System.Collections;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Threading.Tasks;



class Program
{
	//Main
	static void Main(string[] args)
	{
		//出力準備（AutoFlushを切る）
		var sw = new StreamWriter(Console.OpenStandardOutput()){AutoFlush = false};
		Console.SetOut(sw);
		//解答
		Solve();
		//出力終了
		Console.Out.Flush();
	}

	static void Solve()
	{
		//読み込む
		int N = int.Parse(Console.ReadLine());
		int ans = 0;
		for(int i=1; i<N; i++){
			ans += ((N-1)/i);
		}

		Console.WriteLine(ans);
	}
}