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# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;

namespace CABC
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int A = 0;
            int B = 0;
            int C = 0;
            int Counter = 0;

            for (int i = 0; i < N; i++)
            {
                for (int j = 0; j < N; j++)
                {
                    for (int n = 0; n < N; n++)
                    {
                        if ((A * B) + C == N)
                        {
                            Counter++;
                        }
                    }
                }
            }
            Console.WriteLine(Counter);
        }
    }
}