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 <bits/stdc++.h>
using namespace std ;

#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
typedef long long ll ;
typedef unsigned long long ull ;
typedef long double ld ;

const ll MOD = 1E9 + 7, INF = 2E18 + 5 ;
const double PI = 2 * acos(0.0) ;
const long double EPS = 1.0E-14 ;

int main()
{
    ll n, ans = 0, val ;
    cin >> n ;
    val = n - 1 ;
    for (int i = 1; i <= val; i++) {
        ans += (val / i) ;
    }
    cout << ans ;

    return 0 ;
}