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;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.IO.Pipes;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading.Tasks;

namespace AtCorders
{
	public class Program
	{
		static void Main(string[] args)
		{
			string n = Console.ReadLine();
			int l = n.Length;
			int max = int.Parse(n);
			
			var str = new List<char>();
			int ans = 0;
			ans += DFS(str, '0', l, max);
			ans += DFS(str, '3', l, max);
			ans += DFS(str, '5', l, max);
			ans += DFS(str, '7', l, max);

			Console.WriteLine(ans);
		}

		static int DFS(List<char> str, char next, int l, int max)
		{
			str.Add(next);
			try {
				if (str.Count == l) {
					string ss = new string(str.ToArray()).TrimStart('0');
					if (string.IsNullOrWhiteSpace(ss) == false) {
						int num = int.Parse(ss);
						if (num <= max && ss.Contains('0') == false && str.Contains('3') && str.Contains('5') && str.Contains('7')) {
							return 1;
						}
					}

					return 0;
				}

				int count = 0;
				count += DFS(str, '0', l, max);
				count += DFS(str, '3', l, max);
				count += DFS(str, '5', l, max);
				count += DFS(str, '7', l, max);

				return count;
			} finally {
				str.RemoveAt(str.Count - 1);
			}
		}
	}
}