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 Scala (2.11.7) (judge verdict: Accepted)

object Main {

  def main(args: Array[String]): Unit = {
    val sc = new java.util.Scanner(System.in)
    val N = sc.nextLong()

    def solve(): Int = {
      val L = N.toString.length

      def dfs0(i: Int): Int =
        if (i < L - 3)
          dfs0(i+1) + dfs1(i+1, 0, false, false, false)
        else 0

      def dfs1(i: Int, count: Int, seven: Boolean, five: Boolean, three: Boolean): Int =
        if (i < L)
          dfs1(i+1, count + 7 * Math.pow(10, L - i - 1).toInt, true, five, three) +
          dfs1(i+1, count + 5 * Math.pow(10, L - i - 1).toInt, seven, true, three) +
          dfs1(i+1, count + 3 * Math.pow(10, L - i - 1).toInt, seven, five, true)
        else if (seven && five && three && count <= N) 1
        else 0

      val head = N.toString.head.toInt
      if (head >= 7)
        dfs1(1, 7 * Math.pow(10, L - 1).toInt, true, false, false) +
        dfs1(1, 5 * Math.pow(10, L - 1).toInt, false, true, false) +
        dfs1(1, 3 * Math.pow(10, L - 1).toInt, false, false, true) + dfs0(0)
      else if (head >= 5)
        dfs1(1, 5 * Math.pow(10, L - 1).toInt, false, true, false) +
        dfs1(1, 3 * Math.pow(10, L - 1).toInt, false, false, true) + dfs0(0)
      else if (head >= 3)
        dfs1(1, 3 * Math.pow(10, L - 1).toInt, false, false, true) + dfs0(0)
      else dfs0(0)
    }

    println(solve())
  }

}