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

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Solve());
            return;
        }

        private static int Solve()
        {
            var strN = Console.ReadLine();
            var n = int.Parse(strN);
            var len = n.ToString().Length;
            var ans = 0;
            for (int i = 3; i < len; i++) ans += Solve2(i);

            var e = Enumerate(new char[] { '3', '5', '7' }, len)
                .Where(x => int.Parse(x) <= n)
                .Except(Enumerate(new char[] { '3', '5' }, len))
                .Except(Enumerate(new char[] { '5', '7' }, len))
                .Except(Enumerate(new char[] { '3', '7' }, len)).Count();
            return ans + e;
        }

        private static int Solve2(int len)
        {
            var ans = (int)Math.Pow(3, len) - 3 * (int)Math.Pow(2, len) + 3;
            return ans < 0 ? 0 : ans;
        }

        public static IEnumerable<string> Enumerate(IEnumerable<char> items, int k)
        {
            if (k == 1)
            {
                foreach (var item in items)
                    yield return item.ToString();
                yield break;
            }
            foreach (var l in items)
            {
                foreach (var r in Enumerate(items, k - 1))
                {
                    yield return $"{l}{r}";
                }
            }
        }
    }
}