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 {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		
		int count = 0;
		for(int i = 1; i <= n - 1; i++) {
			int n2 = n - i;
			if(n2 == 1) {
				count++;
				break;
			}
			
			if(n2 % 2 == 0) {
				for(int j = 1; j <= Math.sqrt(n2); j++) {
					int temp = n2 / j;
					if(((double)n2 / j) == temp){
						if(temp * temp == n2) count++;
						else count += 2;
					}
				}
			}else {
				for(int j = 1; j <= Math.sqrt(n2); j += 2) {
					int temp = n2 / j;
					if(((double)n2 / j) == temp){
						if(temp * temp == n2) count++;
						else count += 2;
					}
				}
			}
			
			
		}
		
		System.out.println(count);
		
	}

}