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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;

namespace Algorithm
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = Console.ReadLine();
            var dfs = new DfsMaster(int.Parse(n));

            // 2桁未満は対象外だからindex=2から開始
            for (var i = 2; i < n.Length; i++)
            {
                dfs.Keta = i + 1;
                dfs.Execute(0, "");
            }

            Console.WriteLine(dfs.Total);
        }
    }

    public class DfsMaster
    {
        public int Value { get; set; }
        public int Keta { get; set; }
        public int Total { get; set; }

        public DfsMaster(int n)
        {
            this.Value = n;
        }

        public void Execute(int x, string s)
        {
            if (x == Keta)
            {
                var hSet = new HashSet<char>();
                s.ToCharArray().Select(z => hSet.Add(z)).Count();
//                var hSet = s.ToCharArray().Select(z => int.Parse(z.ToString())).ToHashSet();
                if (Value >= int.Parse(s))
                {
                    if (hSet.Count == 3)
                        Total++;
                }
                return;
            }

            Execute(x + 1, s + 3);
            Execute(x + 1, s + 5);
            Execute(x + 1, s + 7);
        }
    }
}