Kobayashi picked watermelons. On the first day, he picked half of the watermelons in the melon field and 10 pieces. On the second day, he picked the remaining half of the watermelons and got 10 pieces. On the third day, he picked 10 pieces and just finished picking them. How many watermelons are there in this melon patch?
小林摘西瓜，第一天摘了瓜地里西瓜的一半又10个，第二天摘了余下的一半有10个，第三天摘了10个正好摘完．这块瓜地共结西瓜多少个．
<gadget id="calculator">10 + 10</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 + 10</gadget>
<output>50</output>

<gadget id="calculator">50 * 2</gadget>
<output>100</output>

<result>100</result>