There are 7 football teams in a certain country, and 3 teams are selected for a single round-robin match every week. After a period of time, the fan Xiao Ming said: "I have watched the match between any two teams." Then , At least how many weeks of games have gone through.
某国有7支足球队伍，每周都会选取其中的3支队伍进行一次单循环比赛，经过若一段时间后，球迷小明说："我已经看过了任意两支队伍之间的比赛了．"那么，至少已经经历了多少周的比赛．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">6 / 2 / 3</gadget>
<output>1</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">7 * 1 * 1</gadget>
<output>7</output>

<result>7</result>