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 Java (OpenJDK 11.0.6) (judge verdict: Time Limit Exceeded)

import java.util.Scanner;

public class Main {
    // A x B + C
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        parseAll(N);
//        System.out.println(parseMultiplication(N));
    }

    private static void parseAll(int n) {
        int count = 0;
        for (int i = 1; i < n; i++) {
            int rest = n - i;
            count += parseMultiplication(rest);
        }
        System.out.println(count);
    }

    private static int parseMultiplication(int n) {
        if (n == 1) {
            return 1;
        }
        int count = 0;
        for (int i = 1;; i++) {
            if (n % i == 0) {
                if (n/i == i) {
                    count++;
                } else {
                    count += 2;
                }
            }
            if (n/(i + 1) < (i + 1)) {
                break;
            }
        }
        return count;
    }
}