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 ll long long 
#define pb push_back 

int main()
{ 
   ios_base::sync_with_stdio(false);
   cin.tie(NULL); 

   ll i,j,t,n,a,b,c,ans=0;
   
   cin>>n;
   for(i=1;i<n;i++)
   {
     for(j=1;i*j<n;j++)
     {
       ans++;
     }
   }
   
   cout<<ans<<endl;
}