There are 15 people participating in a classmate's birthday party (including the students who celebrated the birthday). If every two students shake hands once and do not shake hands repeatedly, how many times will the students shake hands in this party?
某同学生日聚会共有15人参加(包含过生日的同学)，若每两个同学之间握手一次，不重复握手，本次聚会同学们之间共握手多少次．
<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<gadget id="calculator">15 * 7</gadget>
<output>105</output>

<result>105</result>