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)

$tg = []

def build(ts)
  tn = []
  ts.each do |ss|
    s = ss.to_s
    ['3', '5', '7'].each do |c|
      s.length.times do |i|
        ns = s.dup
        ns.insert(i, c)
        tn.push(ns.to_i)
      end
    end
  end
  tn.uniq!

  return tn
end

def solve(ns)
  fig = ns.length
  n = ns.to_i

  ts = [ 357, 375, 537, 573, 735, 753]
  $tg.push(ts)
  for i in 3...fig do
    $tg.push(ts)
    ts = build(ts)
    $tg.push(ts)
  end

  $tg.flatten!
  $tg.sort!.uniq!
  $tg.reverse!
  at = $tg.length
  $tg.length.times do |j|
     if $tg[j] <= n
       at = j
       break
     end
  end
  num = $tg.length - at
  return num
end

ns = gets.chomp
num = solve(ns)
puts num