输出保留 12 位小数的浮点数

Status	Submit By	Time	Memory	Language	Code	Submit At
AC	ALT_sunshuoran	20ms	20.4 MiB	C++14	121 Bytes	2026-9-6 11:08:28
AC	admin	21ms	20.4 MiB	C++14	170 Bytes	2026-8-28 16:22:45
AC	ALT_zhangweichen	21ms	20.4 MiB	C++14	150 Bytes	2026-9-13 16:28:01
AC	ALT_xizhanxuan	21ms	20.4 MiB	C++14	136 Bytes	2026-9-21 21:15:10
AC	ALT_chejunhao	23ms	20.4 MiB	C++14	133 Bytes	2026-10-11 13:13:51
AC	ALT_wujinze	23ms	20.4 MiB	C++14	143 Bytes	2026-10-25 9:18:29