program Project3;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  a: array [1..100] of int64;
  i, i1, i2, i3, i4, i5, i6, i7, i8, i9, i10, i11, i12, i13, i14, j, n, m: integer;
  x, y, min, sum: int64;

begin
  readln(m, n);
  sum := 0;
  min := 10000000000000000;
  for i := 1 to n do begin
    read(a[i]);
    sum := sum + a[i];
  end;
  for i := n + 1 to 15 do
    a[i] := 0;
  for i := 0 to 2 do
    for i1 := 0 to 2 do
      for i2 := 0 to 2 do
        for i3 := 0 to 2 do
         for i4 := 0 to 2 do
          for i5 := 0 to 2 do
            for i6 := 0 to 2 do
              for i7 := 0 to 2 do
                for i8 := 0 to 2 do
                  for i9 := 0 to 2 do
                    for i10 := 0 to 2 do
                      for i11 := 0 to 2 do
                        for i12 := 0 to 2 do
                          for i13 := 0 to 2 do
                            for i14 := 0 to 2 do begin
                               x := a[1] * i + a[2] * i1 + a[3] * i2 + a[4] * i3 + a[5] * i4 + a[6] * i5 + a[7] * i6 + a[8] * i7 + a[9] * i8 + a[10] * i9 + a[11] * i10 + a[12] * i11 + a[13] * i12 + a[14] * i13 + a[15] * i14;
                               y := i + i1 + i2 + i3 + i4 + i5 + i6 + i7 + i8 + i9 + i10 + i11 + i12 + i13 + i14;
                               if((m = x) and (min >= y)) then
                                min := y;
                              end;
                            end;
  if (min <> 10000000000000000) then
    writeln(min)
  else if (sum * 2 < m) then
      writeln(-1)
    else
      writeln(0);

  readln;readln;
end.