Program panel;
Var d,n,i:integer;
    x:byte;
Begin
 readln(n);
 d:=0;
 for i:=1 to n do
  begin
   read(x);
   if (i mod 2 = 1) and (x = 1) then d:=d+1;
   if (i mod 2 = 0) and (x = 0) then d:=d+1;
  end;
 readln;
 if n-d > d then writeln(d)
            else writeln(n-d);
 readln;
End.