Problem:
Score : 400 points

Problem Statement

Find the largest integer that can be formed with exactly N matchsticks, under the following conditions:

Every digit in the integer must be one of the digits A_1, A_2, ..., A_M (1 \leq A_i \leq 9).

The number of matchsticks used to form digits 1, 2, 3, 4, 5, 6, 7, 8, 9 should be 2, 5, 5, 4, 5, 6, 3, 7, 6, respectively.

Constraints

All values in input are integers.

2 \leq N \leq 10^4

1 \leq M \leq 9

1 \leq A_i \leq 9

A_i are all different.

There exists an integer that can be formed by exactly N matchsticks under the conditions.

Input

Input is given from Standard Input in the following format:

N M
A_1 A_2 ... A_M

Output

Print the largest integer that can be formed with exactly N matchsticks under the conditions in the problem statement.

Sample Input 1

20 4
3 7 8 4

Sample Output 1

777773

The integer 777773 can be formed with 3 + 3 + 3 + 3 + 3 + 5 = 20 matchsticks, and this is the largest integer that can be formed by 20 matchsticks under the conditions.

Sample Input 2

101 9
9 8 7 6 5 4 3 2 1

Sample Output 2

71111111111111111111111111111111111111111111111111

The output may not fit into a 64-bit integer type.

Sample Input 3

15 3
5 4 6

Sample Output 3

654

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

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

class Program
{
    private static Dictionary<int, int> canUse;

    static void Main()
    {
        var input = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToList();
        var n = input[0];
        var m = input[0];
        var matches = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToList();

        var need = new int[]
        {
            2, 5, 5, 4, 5, 6, 3, 7, 6
        };

        canUse = new Dictionary<int, int>();
        foreach (var match in matches)
        {
            canUse.Add(match, need[match - 1]);
        }

        var num = Search(n, 0);
        Console.WriteLine(num);
    }

    private static int Search(int limit, int nest)
    {
        var retList = new List<int>();
        foreach (var dic in canUse)
        {
            if (dic.Value > limit)
            {
                retList.Add(-1);
            }

            if (dic.Value == limit)
            {
                retList.Add(dic.Key);
            }

            if (dic.Value < limit)
            {
                var val = Search(limit - dic.Value, nest + 1);
                if (val != -1)
                {
                    retList.Add(int.Parse(dic.Value.ToString() + val.ToString()));
                }
            }
        }

        if (nest == 0)
        {
            foreach (var ret in retList)
            {
                Console.WriteLine(ret);
            }
        }

        return retList.Max();
    }
}