def f
  l = g()
  while c = $<.getc
    case c
    when ?+
      l += g()
    when ?-
      l -= g()
    when ?)
      return l
    end
  end
  l
end

def g
  case c = $<.getc
  when ?(
    f()
  else
    c.to_i
  end
end

p f()