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: Accepted)

import java.util.*;
import java.math.RoundingMode;
import java.math.BigDecimal;
 
 
public class Main{
	public static void main (String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long ans = 0;
		for(int a = 2; a < n-1; a++) {
			int b = 1;
			while(a*b<n&&b<a) {
				ans++;
				b++;
			}
		}
		
		ans*=2;
		for(int a = 1; a <= n-1; a++) {
			if(a*a<n)ans++;
			else break;
		}
		if(n!=2) System.out.println(ans+2);
		else System.out.println(1);
	}
}