A, B, and C are all reading the same story book. There are 100 stories in the book. Everyone starts from a certain story and reads backwards in order. It is known that A has read 50 stories, and B has read 61 stories. C has read 78 stories, so how many stories are there that A, B, and C have read together?
甲、乙、丙都在读同一本故事书，书中有100个故事，每人都从某一个故事开始，按顺序往后读，已知甲读了50个故事，乙读了61个故事，丙读了78个故事，那么甲、乙、丙三人共同读过的故事至少有多少个．
<gadget id="calculator">61 - 100</gadget>
<output>-39</output>

<gadget id="calculator">50 + (-39)</gadget>
<output>11</output>

<result>11</result>