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 Ruby (2.7.1) (judge verdict: Time Limit Exceeded)

def divisor(num)
  result = []
  i = 1
  while (i*i) <= num do
    remainder = num % i
    if remainder == 0
      result << i
      if i*i!=num
          result<<(num/i)
      end
    end
    i += 1
  end
  return result
end
  
  
  
@n=gets.to_i
count=0

for i in 1..@n-1
    v=@n-i
    count+=divisor(v).length
end
p count