program savey;
var
  n,i,l,ans:longint;
  sz:array[1..1000]of char;
function find(a:longint):longint;
var
  t,i:longint;
begin
  if a=1 then begin
    find:=1;
    if sz[1]='0' then sz[1]:='1' else sz[1]:='0';
  end
  else begin
    t:=0;
    if sz[a-1]<>'1' then t:=t+find(a-1);
    for i:=a-2 downto 1 do
      if sz[i]<>'0' then t:=t+find(i);
    if sz[a]='0' then sz[a]:='1' else sz[a]:='0';
    t:=t+1;
    find:=t;
  end;
end;
begin
  assign(input,'savey.in');
  assign(output,'savey.out');
  reset(input);
  rewrite(output);
  readln(n);
  for i:=1 to n do
    read(sz[i]);
  l:=0;
  for i:=n downto 1 do
    if sz[i]='1' then begin
      l:=i;
      break;
    end;
  ans:=0;
  for i:=l downto 1 do
    if sz[i]='1' then ans:=ans+find(i);
  writeln(ans);
  close(input);
  close(output);
end.