After installation Arcadia doesn't run

Hello! I hope anyone will answer. I installed Arcadia, but when I try to run it from command line, it returns me bash: unknown command 'arcadia'. I'm using Linux Mint 17. Thanks!
P.S.
Installed it by running $ gem install arcadia, then tried to run it $ arcadia

[angal]

Hi,
probably you have to install arcadia with sudo (sudo gem install arcadia),
because gem must copy "arcadia" executable into write protected directory as "/usr/bin/", so you can find it when execute from command line.

thank you, I've already solved the problem! I had some problems with Ruby
installed itself, so I reinstalled it totally and then installed Arcadia.
now I can't figure out how to install tk, here's my question on stack
overflow
http://stackoverflow.com/questions/37237089/ruby-tk-installation-in-rbenv-in-linux-mint-17-qiana

2016-05-16 1:19 GMT+03:00 Antonio notifications@github.com:

Hi,
probably you have to install arcadia with sudo (sudo gem install arcadia),
because gem must copy "arcadia" executable into write protected directory
as "/usr/bin/", so you can find it when execute from command line.

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#60 (comment)

[maxie7]

1st step:
sudo gem install arcadia
[sudo] password for max:
Fetching: coderay-1.1.1.gem (100%)
Successfully installed coderay-1.1.1
Fetching: arcadia-1.1.1.gem (100%)
Successfully installed arcadia-1.1.1
Parsing documentation for arcadia-1.1.1
Installing ri documentation for arcadia-1.1.1
invalid options: -SNw2
(invalid options are ignored)
Parsing documentation for coderay-1.1.1
Installing ri documentation for coderay-1.1.1
Done installing documentation for arcadia, coderay after 41 seconds
2 gems installed

2nd step (trying to launch arcadia):
arcadia
/usr/lib/ruby/2.1.0/rubygems/dependency.rb:298:in to_specs': Could not find 'arcadia' (>= 0) among 153 total gem(s) (Gem::LoadError) from /usr/lib/ruby/2.1.0/rubygems/dependency.rb:309:into_spec'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_gem.rb:53:in gem' from /usr/local/bin/arcadia:22:in

'

My OS is Debian Jessie 8.5
What shall i do?