The first and second grade students went to watch the puppet show in the Elf Theater. There were 186 students in the first grade and 235 students in the second grade. There are 500 seats in the theater, how many empty seats are there?
一年级和二年级学生到小精灵剧场看木偶戏，一年级有186人，二年级有235人．剧院共有500个座位，还有多少个空座位？
<gadget id="calculator">500 - 186 - 235</gadget>
<output>79</output>

<result>79</result>