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: Wrong Answer)

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

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			List<long> nm = Console.ReadLine().Split(' ').Select(long.Parse).ToList();
			long n = nm[0];
			long m = nm[1];
			List<long> a = Console.ReadLine().Split(' ').Select(long.Parse).ToList();

			//123456789
			//255456376
			long[] c = new long[] { 2, 5, 5, 4, 5, 6, 3, 7, 6 };
			List<Pair<long, long>> cost = new List<Pair<long, long>>();
			for (int i = 0; i < m; i++) {
				cost.Add(new Pair<long, long>(a[i], c[a[i] -1]));
			}
			cost = cost.OrderByDescending(x => x.F).ToList();

			//174532968
			//234555667
			long[] b = new long[] {1, 7, 4, 5, 3, 2, 9, 6, 8 };
			long key = 1;
			for (int i = 0; i < 9; i++) {
				if (a.Contains(b[i])) {
					key = b[i];
					break;
				}
			}

			long count = n / c[key - 1];
			Queue<long> anss = new Queue<long>();
			for (int i = 0; i < count; i++) {
				anss.Enqueue(key);
			}

			long r = n % c[key - 1];
			while (r != 0) {
				long q = anss.Dequeue();
				r += c[q - 1];
				var first = cost.FirstOrDefault(x => x.F != q && x.S == r);
				if (first != null) {
					anss.Enqueue(first.F);
					r -= first.S;
				} else {
					var second = cost.FirstOrDefault(x => x.F != q && x.S <= r);
					if (second == null) {
						continue;
					}

					anss.Enqueue(second.F);
					r -= second.S;
				}
			}

			List<long> ansss = anss.ToList();
			ansss.Sort();
			ansss.Reverse();
			string ans = "";
			for (int i = 0; i < anss.Count; i++) {
				ans += ansss[i].ToString();
			}

			Console.WriteLine(ans);
		}
	}

	class Pair<T, U> : IComparable<Pair<T, U>> where T : IComparable<T> where U : IComparable<U>
	{
		public T F; public U S;
		public Pair(T f, U s) { this.F = f; this.S = s; }
		public int CompareTo(Pair<T, U> a) => F.CompareTo(a.F) != 0 ? F.CompareTo(a.F) : S.CompareTo(a.S);
		public override string ToString() => $"{F} {S}";
	}
}