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: Wrong Answer)

using System;
class Program
{
	static void Main(string[] args)
	{
        string input = Console.ReadLine();
        int N = int.Parse(input);

        int count = 0;
        int limit = N-1;
        for (int i = 1; i < N; i++)
        {
            for (int j = 1; j < i; j++)
            {
                if(i*j < N)
                {
                    count += 2;
                }
                else
                {
                    break;
                }
            } 
        }

        int x = 1;
        while(true)
        {
            if(x*x < limit)
            {
                x++;
                count++;
            }
            else
            {
                break;
            }
        }
		//出力
		Console.WriteLine(count);
	}
}