This problem doesn't contain real-world specifications about domains, just use the problem statement as a formal document to solve the problem.

The given string s is a domain name if it contains the characters "a"-"z", "0"-"9" and dots. No two dots shoud follow one after another (consecutive). The dots split the given string s into the parts, the last (most right) part should have the length 2 or 3. Domain can't start or end with a dot.

You are given the string s, check if it is domain name.