There are 45 students attending the party. The first boy who came to the meeting shook hands with all the girls. The second boy who came to the meeting was only 1 girl away from shaking hands, and the third boy who came to the meeting was only 2 girls away from shaking hands. ..., the last boy who came to the meeting shook hands with 12 girls. So, how many girls are there in these 45 students?
有45名学生参加聚会，第一个到会的男生和全部女生握手，第二个到会的男生只差1名女生没有握过手，第三个到会的男生只差2名女生没有握过手…，最后一个到会的男生与12名女生握过手．那么，这45名学生中共有多少名女生．
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<gadget id="calculator">45 + 11</gadget>
<output>56</output>

<gadget id="calculator">56 / 2</gadget>
<output>28</output>

<result>28</result>