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++ (Clang 10.0.0) (judge verdict: Accepted)

//Only the Creator has given me strength!

#include<cstdio>

#include<sstream>

#include<cstdlib>

#include<cctype>

#include<cmath>

#include<algorithm>

#include<set>

#include<queue>

#include<stack>

#include<list>

#include<iostream>

#include<fstream>

#include<numeric>

#include<string>

#include<vector>

#include<cstring>

#include<map>

#include<iterator>

#include<bitset>

typedef long long ll;

#define pi 3.1415926535897931159979635

#define pb push_back

#define vctr vector < int >

#define vvtr vector < vctr >

using namespace std;

ll mod=1e7+7;

void fastio() {

    ios::sync_with_stdio(0);

    cin.tie(0);

    cout.tie(0);

}

int main() {

    fastio();

    int n,ans=0;

    cin>>n;

    for(int i=1; i<n; i++){

    ans+=(n-1)/i;

    }

    cout<<ans<<"\n";

    return 0;

}