Nini participated in a sorority meeting with 5 people. After meeting, everyone shook hands with each other. How many times did these people shake hands in total?
妮妮参加共有5人的联谊会，见面后大家互相握手，这些人一共握了多少次手．
<gadget id="calculator">1 - 1</gadget>
<output>0</output>

<gadget id="calculator">5 + 0</gadget>
<output>5</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

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

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

<result>15</result>