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;

namespace AtCoderBeginnerContest118_4
{
    class Program
    {
        public static int[] act = null;
        public static int[] count = null;

        static void Main(string[] args)
        {

            string[] s = Console.ReadLine().Split(' ');

            int N = int.Parse(s[0]);
            int M = int.Parse(s[1]);

            s = Console.ReadLine().Split(' ');
            bool[] number = new bool[6];
            int [] buf = new int[6];

            int[] A = new int[M];

            for (int i = 0; i < M; i++)
            {
                A[i] = int.Parse(s[i]);
            }

            Array.Sort(A);

            for (int i = 0; i < M; i++)
            {
                switch (A[i])
                {
                    case 1:
                        number[0] = true;
                        buf[0] = A[i];
                        break;
                    case 7:
                        number[1] = true;
                        buf[1] = A[i];
                        break;
                    case 4:
                        number[2] = true;
                        buf[2] = A[i];
                        break;
                    case 2:
                    case 3:
                    case 5:
                        number[3] = true;
                        buf[3] = A[i];
                        break;
                    case 6:
                    case 9:
                        number[4] = true;
                        buf[4] = A[i];
                        break;
                    case 8:
                        number[5] = true;
                        buf[5] = A[i];
                        break;
                }
            }

            int tmp = 0;

            for(int i=0;i<6;i++)
            {
                if (number[i])
                    tmp++;
            }

            act = new int[tmp];
            int[] real = new int[tmp];
            int[] lag = new int[act.Length];

            tmp = 0;

            for(int i=0;i<6;i++)
            {
                if(number[i])
                {
                    act[tmp] = i + 2;
                    real[tmp] = buf[i];
                    lag[tmp] = buf[i];
                    tmp++;
                }
            }

            Array.Sort(lag);

            if (check(N,0))
            {
                for(int i=0;i<act.Length;i++)
                {
                    int pos = 0;

                    for(int j=0;j<act.Length;j++)
                    {
                        if(lag[act.Length - i-1] == real[j])
                        {
                            pos = j;
                        }
                    }

                    for(int j=0;j<count[pos];j++)
                    {
                        Console.Write(real[pos].ToString());
                    }
                }
            }

        }

        private static bool check(int rem,int x)
        {

            for(int i=rem/act[x];i>=0;i--)
            {
                int rem2= rem - i * act[x];

                if(rem2 ==0)
                {
                    count[x] = i;
                    return true;
                }

                if (x == count.Length - 1)
                    return false;

                if(check(rem2,x+1))
                {
                    count[x] = i;
                    return true;
                }
            }

            return false;
        }
    }
}