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.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

  public static void main(String[] args) throws Exception {
    try (final var stdin = new InputStreamReader(System.in);
         final var br = new BufferedReader(stdin)) {
      final var n = Integer.parseInt(br.readLine());

      var sum = 0L;
      for (int i = 1; i < n; i++) {
        sum += (n - 1) / i;
      }

      System.out.println(sum);
    }
  }
}