program zad_c;

{$APPTYPE CONSOLE}

uses
  SysUtils;

const
	MAXN = 1000;

var
	a: array [0..MAXN] of integer;
    i, j, m, n, k, ind, ans: integer;

procedure rec(sum, ind, k: integer);
begin
	if (ind > m) then
    	exit;
    if (sum = n) and (k < ans) then
    	ans := k
    else
    if (sum > n) and (ans = maxint) then
    	ans := 0
    else
    begin
    	rec(sum, ind + 1, k);
        rec(sum + a[ind], ind + 1, k + 1);
        rec(sum + a[ind] * 2, ind + 1, k + 2);
    end;
end;

begin
	read(n, m);
    for i := 1 to m do
    	read(a[i]);
    ans := maxint;
    rec (0, 1, 0);
    if (ans = maxint) then
    	writeln('-1')
    else
    	writeln(ans);
    readln;readln;readln;
end.