Mom decided to take Xiaohua to travel to 10 cities by car during the holidays. After checking the map, Xiaohua was surprised to find that there were expressways between any three of these 10 cities, or there were only two cities without expressways. So at least how many expressways have been opened between these 10 cities. (Note: There is at most one expressway between two cities)
妈妈决定假期带小花驾车去10个城市旅游，小花查完地图后惊奇地发现：这10个城市的任意三个城市之间或者都开通了高速公路，或者只有两个城市间没有开通高速路，那么这10个城市间至少开通了多少条高速公路．(注：两个城市间最多只有一条高速公路)
<gadget id="calculator">3 * 2 * 1</gadget>
<output>6</output>

<gadget id="calculator">9 / 6</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">2 * 8 * 10 * (3/2)</gadget>
<output>240</output>

<result>240</result>