var n,i,j,k,head,tail:longint;
    a,g,u:string;
    c:char;     fg:boolean;
    d:array[0..100000]of string;
    f:array[0..100000]of longint;
function check:boolean;
var i,j,k:longint;
begin
 check:=true;
 if g=u then begin fg:=true;exit; end;
 for i:=head to tail do
   if d[i]=g then begin check:=false;exit;end;

end;

procedure go;

begin
for i:=1 to n do
 begin
 if fg then exit;
 g:=d[head];
 if (i>2)and(g[i-2]='0')and(g[i-1]='1') then
   begin
   if g[i]='1' then
     begin g[i]:='0';
           if check then begin
           if fg then exit;
           inc(tail);d[tail]:=g;f[tail]:=f[head]+1;end;
           end;
   if g[i]='0' then
     begin g[i]:='1';
     if check then begin
     if fg then exit;
     inc(tail);d[tail]:=g;f[tail]:=f[head]+1;end;
     end;
   end;
 if (i=2)and(g[i-1]='1') then
   begin
   if g[i]='1' then
     begin g[i]:='0';
           if check then begin
           if fg then exit;
           inc(tail);d[tail]:=g;f[tail]:=f[head]+1;end;
           end;
   if g[i]='0' then
     begin g[i]:='1';
     if check then begin
     if fg then exit;
     inc(tail);d[tail]:=g;f[tail]:=f[head]+1;end;
     end;
   end;
 if (i=1)then  begin
   if g[i]='1' then
     begin g[i]:='0';
           if check then begin
           if fg then exit;
           inc(tail);d[tail]:=g;f[tail]:=f[head]+1;end;
           end;
   if g[i]='0' then
     begin g[i]:='1';
     if check then begin
     if fg then exit;
     inc(tail);d[tail]:=g;f[tail]:=f[head]+1;end;
     end;
   end;
 end;
 inc(head);
 if fg then exit;

end;


Begin
assign(input,'savey.in');reset(input);
assign(output,'savey.out');rewrite(output);
readln(n);i:=0;a:='';u:='';
for i:=1 to n do u:=u+'0';
repeat
 read(c);
 if c='0' then begin inc(i);a:=a+'0';end;
 if c='1' then begin inc(i);a:=a+c;end;
until eof;

head:=0;tail:=0;
fg:=false;
d[0]:=a; f[0]:=0;
repeat

go;

until (head>tail)or fg;
writeln(f[tail]);

close(input);close(output);
end.