using System;
using System.Collections;
using System.Collections.Generic;
 
class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		int[] dp=new int[C+1];
		int Inf=(int)1e9;
		for(int i=0;i<=C;i++)dp[i]=Inf;
		
		dp[0]=0;
		for(int i=0;i<N;i++){
			for(int j=0;j<C;j++){
				if(dp[j]==Inf)continue;
				if(A[i]+j<=C)dp[A[i]+j]=Math.Min(dp[j]+1,dp[A[i]+j]);
			}
		}
		
		Console.WriteLine(dp[C]==Inf?-1:dp[C]);
		
		
		
	}
	int C,N;
	int[] A;
	public Sol(){
		C=ri();
		N=ri();
		A=ria();
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}