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

namespace A {
static class Extensions {
   public static int ToInt(this string str) =>
      int.Parse(str);

   public static int[] readIntArr() =>
      ReadLine().Split(' ').Select(int.Parse).ToArray();

   public static long[] readLongArr() =>
      ReadLine().Split(' ').Select(long.Parse).ToArray();
   
   public static void Fill<T>(this List<T> a, T b) {
      for (var i = 0; i < a.Capacity; i++) {
         a.Add(b);
      }
   } 

   public static void Fill<T>(this T[] a, T b) {
      for (var i = 0; i < a.Length; i++) {
         a[i] = b;
      }
   }
}

class Program {
    static string Smax(string a, string b) {
        if (a.Length > 0 && a[0] == '-') {
            return b;
        }
        else if (a.Length < b.Length) {
            return b;
        }
        else if (a.Length > b.Length) {
            return a;
        }
        else {
            for (var i = 0; i < a.Length; i++) {
                if (a[i] > b[i]) {
                    return a;
                }
                else if (a[i] < b[i]) {
                    return b;
                }
            }
            return a;
        }
    }

    public static void Main(string[] args) {
        var tmp = Extensions.readIntArr();
        var N = tmp[0]; // マッチの数
        var M = tmp[1];
 
        var arr = Extensions.readIntArr().OrderBy(e => -e).ToArray();

        var match = new int[9]{2,5,5,4,5,6,3,7,6};
        /*
          dp[i] ちょうどi本のマッチを使って作れる整数の桁数
        */
        var dp = new int[N + 1];
        dp.Fill(-1);
        dp[0] = 0;

        for (var i = 1; i <= N; i++) {
            foreach (var e in arr) {
                var reqm = match[e - 1];
                if (reqm > i) {
                    continue;
                }
                else if (dp[i - reqm] < 0) {
                    continue;
                }
                else {
                    dp[i] = Max(dp[i], dp[i - reqm] + 1);
                }
            }
        }

        var sb = new StringBuilder();
        var keta = dp.Last();

        var rest = N;
        for (var i = 0; i < keta; i++) {
            foreach(var e in arr) {
                var reqm = match[e - 1];
                if (rest - reqm >= 0 && dp[rest - reqm] == dp[rest] - 1) {
                    sb.Append(e.ToString());
                    rest -= reqm;
                    break;
                }
            }
        }

        WriteLine(sb.ToString());
   }
}

}