program zzn;
type
        rec=record
        st,a:longint;
        end;
        arr=array[1..30]of byte;
var
        head,tail,n,i,j:longint;
        list:array[1..100000]of rec;
        v:array[0..100000000]of boolean;
        aa:arr;
        ch:char;
procedure init;
begin
        assign(input,'savey.in');
        reset(input);
        assign(output,'savey.out');
        rewrite(output);
        readln(n);
        for i:=1 to n do
        begin
        read(aa[i]);
        end;
        list[1].st:=0;
        tail:=1;head:=0;
end;
procedure closef;
begin
        close(input);
        close(output);
end;
function er(c:arr):longint;
var
        i,j:longint;
begin
        j:=0;
        for i:=n downto 1 do
        begin
            j:=j+c[n-i+1]*trunc(exp((i-1)*ln(2)));
        end;
        exit(j);
end;
procedure change(x:longint;var c:arr);
var
        i:integer;
begin
        fillchar(c,sizeof(c),0);
        i:=n+1;
        repeat
             dec(i);
             c[i]:=x mod 2;
             x:=x shr 1;
        until x=0;
end;
function can(x:integer;c:arr):boolean;
var
        i:integer;
begin
        if x=2 then
         begin
            if c[1]=1 then exit(true) else exit(false);
         end;
        for i:=1 to x-2 do if c[i]=1 then exit(false);
        if c[x-1]=0 then exit(false);
        exit(true);
end;
procedure main;
var
        x,y:longint;
        c,b:arr;
begin
        list[1].a:=er(aa);
        fillchar(v,sizeof(v),0);
        v[list[1].a]:=true;
        repeat
         inc(head);
         x:=list[head].a;
         change(x,c);
         for i:=2 to n do
         begin
             b:=c;
             if can(i,b) then
              begin
                  b[i]:=1-b[i];
                  y:=er(b);
                  if not(v[y])then
                  begin
                      v[y]:=true;
                      inc(tail);
                      list[tail].a:=y;
                      list[tail].st:=list[head].st+1;
                      if y=0 then
                       begin
                           writeln(list[tail].st);
                           exit;
                       end;
                  end;
              end else if i<>2 then break;
         end;
         b:=c;
         b[1]:=1-c[1];
         y:=er(b);
         if not(v[y]) then
          begin
              v[y]:=true;
              inc(tail);
              list[tail].a:=y;
              list[tail].st:=list[head].st+1;
              if y=0 then
               begin
                   writeln(list[tail].st);
                   exit;
               end;
          end;
        until head>=tail;
end;
begin
        init;
        main;
        closef;
end.