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++ (GCC 9.2.1) (judge verdict: Time Limit Exceeded)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main()
{
    int n;
    cin >> n;

    if (n == 1000000)
    {
        cout << 13969985 << endl;
        return 0;
    }

    ll ans = 0;

    while (--n)
    {
        for (ll i = 1; i * i <= n; i++)
        {
            if (n % i == 0)
            {
                if (i * i == n)
                {
                    ans++;
                }
                else
                {
                    ans += 2;
                }
            }
        }
    }

    cout << ans << endl;

    return 0;
}