program k22;

{$APPTYPE CONSOLE}

uses
  SysUtils;

const
  MAXIN = 100;

var
  b: array [0..MAXIN] of integer;
  i, n, m, a1, j: integer;

function sum(): int64;
var
   sum1: int64;
   i: integer;
begin
  sum1 := 0;
  for i := 1 to m do
    sum1 := sum1+ b[i];
  sum := sum1 * 2;
end;

function find(n: integer): integer;
var
  a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15: integer;
begin
  if (sum < n) then
    find := -1
  else
  begin
  for a15 := 0 to 2 do
    for a14 := 0 to 2 do
      for a13 := 0 to 2 do
        for a12 := 0 to 2 do
          for a11 := 0 to 2 do
            for a10 := 0 to 2 do
              for a9 := 0 to 2 do
                for a8 := 0 to 2 do
                  for a7 := 0 to 2 do
                    for a6 := 0 to 2 do
                      for a5 := 0 to 2 do
                        for a4 := 0 to 2 do
                          for a3 := 0 to 2 do
                            for a2 := 0 to 2 do
                              for a1 := 0 to 2 do
                                if (a1 * b[1] + a2 * b[2] + a3 * b[3] + a4 * b[4] + a5 * b[5] + a6 * b[6] + a7 * b[7] + a8 * b[8] + a9 * b[9] + a10 * b[10] + a11 * b[11] + a12 * b[12] + a13 * b[13] + a14 * b[14] + a15 * b[15] = n) then
                                begin
                                  find := a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10 + a11 + a12 + a13 + a14 + a15;
                                  exit;
                                end;
  find := 0;
  end;
end;

begin
  readln(n, m);
  j := 1;

  for i := 1 to m do
    read(b[i]);

  writeln(find(n));
  readln;
  readln;
end.