输出保留 3 位小数的浮点数

Status	Submit By	Time	Memory	Language	Code	Submit At
AC	admin	19ms	20.4 MiB	C++14	168 Bytes	2026-8-28 16:17:46
AC	ALT_sunshuoran	20ms	20.4 MiB	C++14	120 Bytes	2026-9-6 11:07:22
AC	ALT_wujinze	21ms	20.4 MiB	C++14	141 Bytes	2026-9-27 20:12:05
AC	ALT_zhangweichen	22ms	20.4 MiB	C++14	147 Bytes	2026-9-13 16:27:06
AC	ALT_xizhanxuan	22ms	20.4 MiB	C++14	136 Bytes	2026-9-21 21:13:57
AC	ALT_chejunhao	22ms	20.4 MiB	C++14	132 Bytes	2026-10-11 13:13:28