In this case the legal ground for the application is the invitation of a natural or legal person. The long-term stay can be certified by the valid invitation letter. The inviter is obliged to take compulsory declaration in the invitation letter in front of the authority that he will provide during the stay of the applicant: lodgement, he will cover the costs of his living, he will cover the costs of his eventual medical treatment and his return to his country of origin. The invitation letter is sealed and stamped by Immigration Office. The invitation letter is valid for a maximum 365 days which is not allowed to prolong.