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;
 
// in-short-use macros
 
#define all(c) (c).begin(),(c).end()
#define ll long long int
#define ld long double
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define mod 1000000007
#define PI 3.14159265
#define sizes 1000010
 
//main function here
 
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	ll n,ans =0 ;
	cin>>n;
	for(ll i=1;i<=n-1;i++)
	{
		ans+=n/i;
		if(n%i==0)
			ans--;
	}
	cout<<ans<<"\n";
	return 0;
}