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>
/*
CE 头文件 
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>

*/
using namespace std;
#define rep(i,a,n) for (int i=a;i<=n;i++)
#define per(i,a,n) for (int i=n;i>=a;i--)
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
#define mem(a,b) memset(a,b,sizeof (a))
#define ios std::ios::sync_with_stdio(false); std::cin.tie(0); std::cout.tie(0);
// ios和scanf,printf不能混用.即用ios必须全部cin,cout. 
typedef vector<int> VI;
typedef long long ll;
typedef pair<int,int> PII;
const ll mod=1000000007;

ll ksm(ll a,ll b){ll res=1;a%=mod;for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
const int N=110;
PII a[N];
int n;
int divide(int x){
	int sum=0;
	for(int i=1;i<=sqrt(x);i++){
		if(x%i==0){
			sum+=2;
		}
		if(i*i==x)sum--;
	}
	return sum;
}
int main(){
	scanf("%d",&n);
	ll ans=0;
	rep(i,1,n-1){
		ans=ans+1ll*divide(i);
	}
	printf("%lld",ans);
    return 0;
}