program luojibiaodashi;
var
  s:string;
  i:integer;
  bool,b:boolean;
begin
  assign(input,'expressa.in');
  reset(input);
  assign(output,'expressa.out');
  rewrite(output);
  readln(s);
  bool:=true;
  for i:=1 to length(s) do
  begin
    if ((s[i]>='a') and (s[i]<='z')) or ((s[i]>='A') and (s[i]<='Z'))
      or (s[i]='~') or (s[i]='*') or (s[i]='+') or (s[i]='(') or (s[i]=')')
    then b:=true
    else b:=false;
    if b=false
      then bool:=false
  end;
  if bool
    then writeln('yes')
    else writeln('no');
  close(input);
  close(output)
end.