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 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner scanner =new Scanner(System.in);
		int N = scanner.nextInt();
		long ans = 0;
		for (int i = 1; i < N; i++) {
			int M = N-i;
			for (int j = 1; j <= Math.sqrt(M); j++) {
				if (M % j == 0) {
					if ((M / j) == j) {
						ans++;
					}else{
						ans += 2;
					}
				}
			}
		}

		System.out.println(ans);
		scanner.close();
	}

}