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: Time Limit Exceeded)

#include<bits/stdc++.h>
#define ll long long
#define vi vector<int>
#define vll vector<ll>
#define F first
#define S second
#define pb push_back
#define f(i,s,n) for(int i=(int)s;i<=(int)n;++i)
#define Fast ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
using namespace std;
void solve()
{
	ll n;cin>>n;
	ll k=n;
	ll ans=0;
	for(int i=1;i<n;i++){
		k=n-i;
		int cnt=0;
		for(ll J=1;J*J<=k;J++){
			if(k%J==0){
				if(J!=k/J){
					cnt+=2;
				}
				else
					++cnt;
			}
		}
		ans+=(cnt);
	}
	cout<<ans<<'\n';
}
int main()
{	Fast;
//	int t;cin>>t;
//	while(t--)
	solve();
}