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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Text.RegularExpressions;

namespace C
{
    class Program
    {
        static int maxLength = 9;
        static string[][] memo = new string[10][];

        static void Main()
        {
            var input = int.Parse(Console.ReadLine());
            var count = 0;
            var strArr = Generate(maxLength);

            foreach (var line in memo)
            {
                foreach (var val in line)
                {
                    if (float.Parse(val) < input)
                    {
                        var cArr = val.ToCharArray();
                        var flag = new bool[3];
                        foreach (var c in cArr)
                        {
                            switch (int.Parse(c.ToString()))
                            {
                                case 3:
                                    flag[0] = true;
                                    break;
                                case 5:
                                    flag[1] = true;
                                    break;
                                case 7:
                                    flag[2] = true;
                                    break;
                                default:
                                    break;
                            }

                            if (flag.All(x => x == true))
                            {
                                count++;
                                break;
                            }
                        }
                    }
                }
            }

            Console.WriteLine(count);
        }

        //繋げる関数
        static string[] Connect(string[] strArr)
        {
            var retArr = new List<string>();
            foreach (var str in strArr)
            {
                retArr.Add(str + "3");
                retArr.Add(str + "5");
                retArr.Add(str + "7");
            }

            return retArr.ToArray();
        }

        static string[] Generate(int length)
        {
            if (length != maxLength && memo[length] != null)
            {
                return memo[length];
            }
            if (length == 0)
            {
                var strArr = new string[] { "3", "5", "7" };
                memo[length] = strArr;
                return Connect(strArr);
            }
            else
            {
                var strArr = Generate(length - 1);
                memo[length] = strArr;
                return Connect(strArr);
            }
        }
    }
}