GF

Every once in a while someone makes a competitive programming server. Today, we're inviting you to join one of them Our server is called **GF** (short for **G** enerating **F** unction, or, perhaps, a **g** irl **f** riend? Who knows!). We are a Div. 1 community and discussion space. Your **rating** must be **1900 or more** to join. Originally posted on codeforces: https://codeforces.com/blog/entry/145423