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: Accepted)

#include <iostream>

#include <cstdio>

using namespace std;



typedef long long ll;

ll n, c;

int main()

{

    ll i, t;


    cin >> n;

    for (i = 1; i <= n; i++) {

        t = n / i;

        if (t * i == n) t--;

        c += t;

    }

    cout << c << endl;

    return 0;

}