There are 6 students from Zhongxin International Experimental School participating in the city speech contest. If these 6 students need to high-five each other in order to cheer each other up, how many high-fives should they have in total?
中欣国际实验学校有6名同学参加市演讲比赛，如果这6名同学为了给对方加油，每两人都需要击掌一次，那么一共要击掌多少次？
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>