Russian citizens can be in Sri Lanka 30 days from the date of arrival. The period of stay can be extended to a maximum of 3 months. To do this, go to the Immigration Office in Colombo and file a request. To go better by 9 am - then by the 12th day you will already have an extension.

If you need to stay in the country for more than 3 months - you should either fly out of the country and apply for a visa anew, or start a business, register your company and receive a business visa. The price of a business visa is 1500 USD per year per person (including infants).