Two children toss a coin and decide the winner by heads and tails, and hand over a pebble once they lose. They each have a pile of stones of the same number. After a number of games, one of the children wins three times, and the other child has seven more stones.
两小孩掷硬币，以正、反面定胜负，输一次交出一粒石子．他们各有数量相等的一堆石子，比赛若干次后，其中一个小孩胜三次，另一个小孩石子多了7个，那么一共掷了多少次硬币．
<gadget id="calculator">7 + 3 + 3</gadget>
<output>13</output>

<result>13</result>