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 {

		static long mod = 1000000007;

		public static void main(String[] args) {
			// AtCoder_C
			Scanner sc = new Scanner(System.in);
			int N = sc.nextInt();
    	    // Scannerクラスのインスタンスをクローズ
    		sc.close();

    		long ans=0;

    		for(int C=1; C<N; C++) {
    			int AB = N-C;
    			for(int A=1; A<=Math.sqrt(AB); A++) {
    				if(AB%A==0) {
    					ans++;
    					if(AB/A != A) {
        					ans++;
    					}
    				}
    			}
    		}
    		System.out.println(ans);
    	}
    }