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: Wrong Answer)

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <string>
#include <vector>
using namespace std;

#define FOR(i, a, b) for (long i = a; i < b; ++i)
#define REP(i, n) for (long i = 0; i < n; ++i)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

int main() {
  long n;
  cin >> n;
  vector<long> A(10000001, 0);
  FOR(i, 1, 1000000) {
    FOR(j, i + 1, 1000000 / i) {
      if (i * j < 1000001)
        A[i * j] += 2;
    }
    if (i * i < 1000001)
      A[i * i] += 1;
  }
  long ans = 0;
  FOR(i, 1, n) { ans += A[i]; }
  cout << ans << endl;
}