There are 11 students planning to organize a Go game. They are going to be divided into two groups, and each group will play a single round-robin game. How many games do they need at least?
有11个同学计划组织一场围棋比赛，他们准备分为两组，每组进行单循环比赛，那么他们最少需要比赛多少场？
<gadget id="calculator">11 - 1</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">11 * 5</gadget>
<output>55</output>

<result>55</result>