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>
using namespace std;

int main() {
	int N;
	cin >> N;
	int total = 0;
	for (int i = 1; i < N; i++) {
		for (int j = 1; j * j <= N - i; j++) {
			if ((N - i) % j == 0 && j * j == (N - i)) {
				total++;
			}
			else if ((N - i) % j == 0 && j * j != (N - i)) {
				total += 2;
			}
		}
	}
	cout << total << endl;
}