Privacy policy

To make this site work properly, we sometimes place small data files called cookies on your device. Most big web-sites do this too.

What are cookies

A cookie is a small text file that a web-site saves on your computer or mobile device when you visit the site. It enables the web-site to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don't have to keep re-entering them whenever you come back to the site or browse from one page to another.

How do we use cookies

A number of our pages use cookies to remember:

  • your login information after you sign in to make it possible for you to submit solutions, see their results, and communicate with other users,
  • your display preferences, such as contrast color settings or font size,
  • if you have agreed (or not) to our use of cookies on this site.

Enabling cookies is not strictly necessary for the web-site to work, but without cookies you will not be able to submit your own solutions and it will be only possible to browse information that are based on other users' submissions. You can delete or block these cookies, but if you do that the above features of this site may not work as intended. The cookie-related information is fully under our control. These cookies are not used for any purpose other than those described here.

How to control cookies

You can control and/or delete cookies as you wish - for details, see You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.