Language: Erlang

Source code:

-module(spbctf_2). -export([main/1]). %ord returns ASCII code of character, e.g. ord("a") return 97 ord(A) -> hd(A). main(_) -> io:format("Ave!\n"), Flag = case io:fread("Give me the flag: ", "~s") of {ok, [R|_]} -> R; {error, _} -> io:format("Error while reading your string"), erlang:exit(error_read) end, Caesar = fun(A) -> (A - ord("a") + 3) rem 26 + ord("a") end, Caesared = lists:map(Caesar, Flag), case string:equal(Caesared, "yhqlylglkdfnhulfl") of true -> io:format("Right\n"); false -> io:format("Wrong\n") end.

How to run Erlang:
1. Download Erlang from erlang.org
2. Run in console: escript task.erl