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>

#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define pb(x) emplace_back(x)
#define forn(i,N) for(int i=0;i<N;i++)
#define rep(i,x,N) for(int i=x;i<=N;i++)
#define ar array

using namespace std;
using ll=long long int;
using ld=long double;
using vi=vector<int>;
using vll=vector<ll>;
using vd=vector<double>;
using vvi=vector<vi>;
int ctoi(char c) {return c-'0';}
int slen(string s) {return s.length();}
int vsize(vi a) {return (int)a.size();}
int in() {int x;cin>>x;return x;}
void tf(bool ok) {cout<<(ok ? "YES" : "NO")<<endl;}

//https://atcoder.jp/contests/abc179/tasks/abc179_c

void rrrrrrrrrrrrrresi() {
  int N;
  cin>>N;
  ll ans=0;
  for(int i=1;i<N;i++) {
    for(int j=1;j*i<N;j++) {
      ans++;
    }
  }
  cout<<ans<<endl;
}

int main() {
//freopen("input.txt","rt",stdin);
ios::sync_with_stdio(false);
cin.tie(nullptr);

int Q=1;
//cin>>Q;
while(Q--)
  rrrrrrrrrrrrrresi();
return 0;
}