var
ANS : array[1..100000] of integer;
k: integer;

type
  TCoinsSet = array[1..16] of integer;


  function AmountCoins(N: integer; M: integer; const A: TCoinsSet): integer;
  var
    MinAmount, CurAmount: integer;
    Sum: integer;

    k := 1;

    procedure Backtracking(NCoin: integer);
    var
      i: integer;
    begin
      if NCoin > M then
        Exit;
      if Sum > N then
        exit;

      for i := 0 to 2 do
      begin
        if Sum = N then
        begin
          if CurAmount < MinAmount then
            MinAmount := CurAmount;
        end;
        Backtracking(NCoin + 1);
        Inc(CurAmount);
        Sum := Sum + A[NCoin];
        ANS[k] := A[NCoin];
        Inc(k);
      end;

      Dec(CurAmount, 3);
      Sum := Sum - 3 * A[NCoin];
    end;

  begin
    MinAmount := M + M + 1;
    CurAmount := 0;
    Sum := 0;
    Backtracking(1);
    if MinAmount > M + M then
      MinAmount := 0;
    AmountCoins := MinAmount;
  end;

var
  N: integer;
  M: integer;
  A: TCoinsSet;
  Summ: integer;
  i, j, ans1: integer;
begin
  Summ := 0;

  readln(N, M);
  for i := 1 to M do
  begin
    Read(A[i]);
    Summ := Summ + A[i];
  end;
  if Summ + Summ < N then
  begin
    writeln('-1');
  end
  else
  begin
    ans1 := AmountCoins(N, M, A);
    writeln(ans1);
    for i := 1 to 10000 do
      begin
      write(ANS[i], ' ');

      if (ANS[i] = 0) then
        begin
          //writeln(ANS[i], ' i ', i, ' ans1 ', ans1);
          for j := i-ans1 to i-1 do
            begin
            writeln('!!!!!!!!!');
              write(ANS[j], ' ');
            end;
          break;
        end;
      end;
  end;

end.