program savey(input,output);

type
  re=record
    deep,n:longint;
  end;

var
  n,i,len,dp,rec:longint;
  ch:char;
  boo:array[0..16777216]of boolean;
  q:array[1..1000000]of re;

function expand(a:re):boolean;
  var
    i,t:longint;
  begin
    t:=a.n xor (1 shl (n-1));

    if t=0 then
      exit(true);

    if (t<16777216) and not(boo[t]) then
    begin
      inc(len);
      boo[t]:=true;
      q[len].deep:=a.deep+1;
      q[len].n:=t;
    end;

    for i:=n-1 downto 1 do
      if a.n shr i=1 then
      begin
        t:=a.n xor (1 shl (i-1));

        if t=0 then
          exit(true);

        if (t<16777216) and not(boo[t]) then
        begin
          inc(len);
          boo[t]:=true;
          q[len].deep:=a.deep+1;
          q[len].n:=t;
        end;
      end
      else if a.n shr i>1 then
        break;

    exit(false);
  end;

begin
  assign(input,'savey.in');
  reset(input);
  assign(output,'savey.out');
  rewrite(output);

  readln(n);

  for i:=1 to n do
  begin
    read(ch);
    rec:=rec shl 1;
    if ch='1' then
      rec:=rec+1;
    read(ch);
  end;

  if rec=0 then
  begin
    writeln(0);
    close(input);
    close(output);
    halt;
  end;

  q[1].n:=rec;
  q[1].deep:=0;
  if (rec<16777216) then
    boo[rec]:=true;
  i:=1;
  dp:=0;
  len:=1;
  repeat
    while q[i].deep=dp do
    begin
      if expand(q[i]) then
      begin
        writeln(dp+1);
        close(input);
        close(output);
        halt;
      end;
      inc(i);
    end;

    inc(dp);
  until 1=2;
end.