There is a peach tree on the top of a certain mountain. A monkey eats a peach. It eats half and half of the tree on the first day, and the remaining half and half of the tree on the second day. There are still 19 peaches left on the tree. How many peaches were there originally on this tree?
某山顶有棵桃树，一只猴子吃桃子，第一天吃了树上的一半又半个，第二天吃了树上剩下的一半又半个，树上还剩下19个桃子，这棵树上原来有多少个桃子？
<gadget id="calculator">19 + 0.5</gadget>
<output>19.5</output>

<gadget id="calculator">19.5 * 2</gadget>
<output>39</output>

<gadget id="calculator">39 + 0.5</gadget>
<output>39.5</output>

<gadget id="calculator">39.5 * 2</gadget>
<output>79</output>

<result>79</result>