var s,t:char;
    n,i,b,w,ans:integer;
begin
  readln(n);
  s:='.';
  b:=0; w:=0;
  ans:=0;
  for i:=1 to n do begin
    read(t);
    if s=t and t='#' then inc(b);
    if s=t and t='.' then inc(w);
    if s<> and t='#' then begin
      if b<w then inc(ans,b)
      else inc(ans,w);
      b:=1;
      w:=0
    end;
    if s<>t and t='.'then inc(w);
    s:=t
  end;
  write(ans)
end.