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 Julia (1.4.0) (judge verdict: Time Limit Exceeded)

using Primes
function F()
  N = parse(BigInt,readline())
  c = 0
  for i =1:N-1
    if i==1
      c += 1
    else
      s = collect(factor(i))
      S = 1
      for j = 1:length(s)
        S *= (s[j][2]+1)
      end
      c += S
    end
  end
  println(c)
    
  
end
F()