program soma_ab ;

var
  i, soma : integer ;
  li,ls   : integer ;

begin
  write ('Limite inferior: ') ;
  read (li) ;

  write ('Limite superior: ') ;
  read (ls) ;

  if (li <= ls) then
  begin
    soma := 0 ;
    i := li ;

    while (i <= ls) do
    begin
      soma := soma + i ;
      i := i+1 ;
    end ;
  end
  else // se li > ls
  begin
    soma := 0 ;
    i := ls ;
    while (i <= li) do
    begin
      soma := soma + i ;
      i := i+ 1 ;
    end;  
  end ;

  writeln ('a soma de ', li,' a ', ls,' vale: ', soma) ;
end.