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 int[] dp = new int[10001];

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

			//123456789
			//255456376
			int[] c = new int[] {0, 2, 5, 5, 4, 5, 6, 3, 7, 6 };
			for (int i = 2; i <= n; i++) {
				int max = -1;
				for (int j = 0; j < m; j++) {
					if (i - c[a[j]] < 0 || dp[i - c[a[j]]] == -1) {
						continue;
					}

					max = Math.Max(max, dp[i - c[a[j]]] + 1);
				}

				dp[i] = max;
			}

			a.Sort();
			a.Reverse();
			StringBuilder ans = new StringBuilder();
			int k = dp[n];
			int count = n;
			for (int i = 0; i < k; i++) {
				for (int j = 0; j < m; j++) {
					if (count >= 0 && count - c[a[j]] >= 0 && dp[count] - 1 == dp[count - c[a[j]]]){
						ans.Append(a[j].ToString());
						count -= c[a[j]];
						break;
					}
				}
			}

			Console.WriteLine(ans.ToString());
		}
	}

	
}