Problem:
Score : 300 points

Problem Statement

You are given an integer N. Among the integers between 1 and N (inclusive), how many Shichi-Go-San numbers (literally "Seven-Five-Three numbers") are there?

Here, a Shichi-Go-San number is a positive integer that satisfies the following condition:

When the number is written in base ten, each of the digits 7, 5 and 3 appears at least once, and the other digits never appear.

Constraints

1 \leq N < 10^9

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the number of the Shichi-Go-San numbers between 1 and N (inclusive).

Sample Input 1

575

Sample Output 1

4

There are four Shichi-Go-San numbers not greater than 575: 357, 375, 537 and 573.

Sample Input 2

3600

Sample Output 2

13

There are 13 Shichi-Go-San numbers not greater than 3600: the above four numbers, 735, 753, 3357, 3375, 3537, 3557, 3573, 3575 and 3577.

Sample Input 3

999999999

Sample Output 3

26484

Solution in Ruby (2.3.3) (judge verdict: Accepted)

N = gets.to_i
digit_count = N.to_s.size
candidate_list = [['3'], ['5'], ['7']]
current_digit_candidate_list = candidate_list
(digit_count - 1).times do
  current_digit_candidate_list =
    current_digit_candidate_list.flat_map do |candidate|
      ['3', '5', '7'].map { |c| [c] + candidate }
    end
  candidate_list = candidate_list + current_digit_candidate_list
end
answer = candidate_list
  .select { |ca| ca.uniq.size === 3 }
  .map { |ca| ca.join('').to_i }
  .count { |n| n <= N }
puts answer