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;
using System.Text;
static class Program{
	const int mod=1000000007;
	const long o=1;
	static void Main(){
		Sc sc=new Sc();
		int[] s=sc.Ia;
		int[] a=sc.Ia;
		long[] dp=new long[s[0]+1];
		string[] dp2=new string[s[0]+1];
		bool[] b=new bool[10];
		int[] h=new int[]{0,2,5,5,4,5,6,3,7,6};
		for(int i=0;i<s[1];i++){b[a[i]]=true;}
		dp[0]=1;
		for(int i=2;i<=s[0];i++){
			for(int j=1;j<10;j++){
				if(b[j]&&h[j]<=i&&dp[i-h[j]]>0){
					if(dp[i]<dp[i-h[j]]+1){
						dp[i]=dp[i-h[j]]+1;
						dp2[i]=dp2[i-h[j]]+j.ToString();
					}
					else if(dp[i]==dp[i-h[j]]+1&&string.Compare(dp2[i-h[j]]+j.ToString(),dp2[i])==1){
						dp2[i]=dp2[i-h[j]]+j.ToString();
					}
				}
			}
		}
		Console.WriteLine(dp2[s[0]]);
	}
}

public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()).Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
}