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: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
class c{
    public static void Main(){
        int n = int.Parse(Console.ReadLine());
        int ans = 0;
        for(int i=1; i<n; i++){
            for(int j=1; j<=Math.Sqrt(i); j++){
                if(i%j == 0){
                    if((i/j) == j){
                        ans++;
                    }
                    else{
                        ans += 2;
                    }
                }
            }
        }
        Console.WriteLine(ans);
    }
}