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)

#pragma region header
#include <algorithm>
#include <bitset>
#include <tuple>
#include <cstdint>
#include <cctype>
#include <assert.h>
#include <time.h>
#include <stdlib.h>
#include <stdio.h>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#include <math.h>
#include <cstring>
#include <array>
// ===============================================================
//using系
#pragma region header
using namespace std;
using lint = long long;
using ld = long double;
using ulint = unsigned long long;
const int dx[] = { 1,0,-1,0 };
const int dy[] = { 0,1,0,-1 };
constexpr lint mod = 1000000007;
constexpr long double pi = 3.141592653589793238462643383279;
#pragma endregion
// ========================================================================
//define
#define INF (lint)10000000000000000;
#define mod (int)1000000007
#pragma region header
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
	if (lhs > rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
	if (lhs < rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
#pragma endregion
#pragma endregion



int main(void) {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	lint cnt = 0;
	for (int i = 1; i < n; i++) {
		int s = n;
		s -= i;
		lint ans = 0;
		for (int j = 1; j * j <= s; j++) {
			if (s % j == 0) {
				ans++;
				if (j * j != s) ans += 1;
			}
		}
		cnt += ans;
	}
	cout << cnt << endl;

	return 0;
}