title: How to get only the last value of the series output of an expression?
body: <p>I don't need a whole array of this expression, just its very recent (current) value. How to modify its code?</p>
  <pre><code>UpperBollinger = ta.sma(close, 20) + 2 * ta.stdev(close, 20)
  </code></pre>
  <p>(Of course, I can use it to get the same for the lower band.)</p>