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)

/*author @dhanush*/

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define boost ios_base::sync_with_stdio(false);cin.tie(NULL)
#define pb push_back
#define se second
#define fi first
ll MOD = 1e9 + 7;
vector<ll>adj[100005];
ll factor[1000005];
void build(ll n)
{
  factor[1] = 1;
  for (int i = 2; i <= 1000000; i++)
  {
    factor[i] = 0;
  }
  for (ll i = 2; i <= 1000000; i++)
  {
    factor[i] += 2;
    for (ll j = i + i; j <= 1000000; j += i)
    {
      factor[j] += 1;
    }
  }
}
void icchhipadey()
{

  ll n;
  cin >> n;
  ll ans = 0;
  build(n);
  for (ll i = 1; i <= n - 1; i++)
  {
    ll xx = n - i;
    ll cnt = 0;
    // if (xx == 1)
    // {
    //   cnt = 1;
    // }
    // else
    // {
    //   cnt = 2;
    // }
    // for (ll j = 2; j * j <= xx; j++)
    // {
    //   if (xx % j == 0)
    //   {
    //     cnt++;
    //     if (xx / j != j)
    //     {
    //       cnt++;
    //     }
    //   }
    // }
    ans += factor[xx];

  }
  cout << ans << endl;

}


int main()
{


  boost;
  icchhipadey();
}