rails not working in ruby on rails

expertly@AECUTE ~/Documents/RUBY/timetable $ rails s

/home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:80:in rescue in block (2 levels) in require': There was an error while trying to load the gem 'uglifier'. (Bundler::GemRequireError) from /home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:76:inblock (2 levels) in require' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in each' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:inblock in require' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in each' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:inrequire' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/bundler-1.11.2/lib/bundler.rb:99:in require' from /home/expertly/Documents/RUBY/timetable/config/application.rb:7:in' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:78:in require' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:78:inblock in server' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:75:in tap' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:75:inserver' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:39:in run_command!' from /home/expertly/.rvm/gems/ruby-2.2.4/gems/railties-4.2.5/lib/rails/commands.rb:17:in' from bin/rails:4:in require' from bin/rails:4:in'

please help me for this problem.