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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;
using static System.Console;
using System.Text;
using System.IO;
using static System.Math;
using System.Numerics;

namespace AtCoder
{
    class Program
    {
        static public long[] Sarray() { return ReadLine().Split().Select(long.Parse).ToArray(); }
        static public List<long> Slist() { return ReadLine().Split().Select(long.Parse).ToList(); }
        static long Mod = (long)1e9 + 7;
        static void Main(string[] args)
        {
            SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
            Solve();
            Out.Flush();
            Read();
        }
        static void Solve()
        {
            var NM = Sarray();
            var N = NM[0];
            var M = NM[1];
            var Ai = Slist();
            if (Ai.Contains(9)) { Ai.Remove(6); }
            if (Ai.Contains(5)) { Ai.Remove(3); Ai.Remove(2); }
            if (Ai.Contains(3)) { Ai.Remove(2); }

            var pair = new Dictionary<long, long>()
            {
                { 1, 2 }, { 2, 5 }, { 3, 5 }, { 4, 4 }, { 5, 5 },
                { 6, 6 }, { 7, 3 }, { 8, 7 }, { 9, 6 }
            };
            var AiPair = new List<(long n, long c)>();
            foreach (var a in Ai)
                AiPair.Add((a, pair[a]));
            var min = AiPair.First(a => a.c == AiPair.Min(c => c.c));
            AiPair = AiPair.Where(a => a.c % min.c != 0).Select(a => (a.n, a.c - min.c)).ToList();
            var left = AiPair.Where(a => a.n > min.n).OrderByDescending(a => a.n).ToList();
            var right = AiPair.Where(a => a.n < min.n).OrderByDescending(a => a.c).ToList();
            var keta = N / min.c;
            for (keta = N / min.c; 0 < keta; --keta)
            {
                used = new long[AiPair.Count];
                if (dfs(N - keta * min.c, 0, left.Concat(right).ToList())) break;
            }
            var ans = string.Empty;
            for (var i = 0; i < left.Count; ++i)
                ans += new string(left[i].n.ToString()[0], (int)used[i]);
            ans += new string(min.n.ToString()[0], (int)(keta - used.Sum()));
            for (var i = 0; i < right.Count; ++i)
                ans += new string(right[i].n.ToString()[0], (int)used[left.Count + i]);
            WriteLine(ans);
        }
        static long[] used;
        static bool dfs(long rem, int i, List<(long n, long c)> pair)
        {
            if (rem == 0) return true;
            if (rem < 0 || pair.Count <= i) return false;
            var cst = pair[i].c;

            for (var k = rem / cst; 0 <= k; --k)
            {
                if (dfs(rem - k * cst, i + 1, pair))
                {
                    used[i] = k;
                    return true;
                }
            }
            return false;
        }
    }
}