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
ll m=1e9+7;
ll power(ll a,ll b)
{
	ll res=1;
	while(b>0)
	{
		if(b&1) res=(res*a)%m;
		b/=2;
		a=(a*a)%m;
	}
	return res;
}
int main() 
{
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
	int t=1;
	//cin>>t;
	while(t--)
	{
		int n;
		cin>>n;
		int c=0;
		for(int a=1;a<=n;a++) 
		{
			c+=n/a;
			if(n%a==0) c--;
		}
		cout<<c<<endl;
	}
	return 0;
}