ISO C99 defined %Lf to output long doubles with printf.

However, printf is implemented by C standard libraries, and some evidence show Codeforces is using old style msvcrt, which does not support %Lf.

In fact, long double is not very useful in Codeforces. Since Codeforces usually allow answer with 10^- 6 error to be accepted, the precision of long double is useless.

thanks orz_liuwei — you are correct.