yle="text-indent: 21pt" align="left"><span style="font-size: medium">第[2, M+1]行每行两个整数o1, o2，表示有一条从o1到o2的边。</span></div></div></div></div></div></div><div class="row"><div class="column"><h4 class="ui top attached block header">输出格式</h4><div class="ui bottom attached segment font-content"><div style="position: relative; overflow: hidden;"><div class=content><div style="text-indent: 21pt" align="left"><span style="font-size: medium">一个浮点数，保留小数�