Maybe it's not appropriate to ask such question here, but I can't find the answer by google and don't know where to ask this question. Please don't downvote...
I registered AtCoder Beginner Contest, then I changed my mind and wanted to participate in Regular Contest, but couldn't find a way to register since I can't register both contests.
Does anyone know how to solve this? Thanks in advance.

As everyone knows, it's forbidden to submit code containing "%lld". Once I thought this is because "%lld" doesn't work in Codeforces' system. However, I happened to submit code using (#define LLD "%l" "ld") and use the macro LLD for printf, and it works all the time just like "%I64d", does anyone know the reason? Does it really always work with "%lld"?