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: Accepted)

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

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = ReadArrayInt();
            var N = input[0];
            var M = input[1];
            var A = ReadArrayInt();
            Array.Sort(A);
            Array.Reverse(A);
            var matNum = new int[] { 0, 2, 5, 5, 4, 5, 6, 3, 7, 6 };
            var dp = new int[N + 1];
            for (int i = 1; i <= N; i++)
            {
                dp[i] = int.MinValue;
                for (int j = 0; j < M; j++)
                {
                    if (matNum[A[j]] <= i)
                    {
                        dp[i] = Math.Max(dp[i - matNum[A[j]]] + 1, dp[i]);
                    }
                }
            }
            var rem = N;
            var ans = new int[dp[N]];
            for (int i = 0; i < dp[N]; i++)
            {
                for (int j = 0; j < M; j++)
                {
                    if (matNum[A[j]] <= rem && dp[rem - matNum[A[j]]] == dp[rem] - 1)
                    {
                        ans[i] = A[j];
                        rem -= matNum[A[j]];
                        break;
                    }
                }
            }

            Console.WriteLine(string.Join("", ans));
            Console.ReadLine();
        }

        static string Read() { return Console.ReadLine(); }
        static int ReadInt() { return int.Parse(Read()); }
        static long ReadLong() { return long.Parse(Read()); }
        static int[] ReadArrayInt() { return Read().Split(' ').Select(s => int.Parse(s)).ToArray(); }
        static long[] ReadArrayLong() { return Read().Split(' ').Select(s => long.Parse(s)).ToArray(); }
    }
}