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 endl            "\n"
#define sz(x)          (int) (x.size())
#define all(v)          v.begin(), v.end()
#define isOdd(n)       (n&1)
#define pow(n, m)      (ll)powl(n, m)
#define clr(x, val)     memset(x, val, sizeof(x))

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;


int main()
{
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);

    int n; cin >> n;
    ll c = 0;
    for(int i = 1; i < n; i++){
        ll k = i;
        while(k < n) c++, k += i;
    }
    cout << c;
    return 0;
}