Nikitosh and Sauron-tetrahedron

A dark tetrahedron's size is said to be N if each of its edges consists of N segments. To destroy a dark tetrahedron of size N, you have to erase at least N segments (you can't destroy a dark tetrahedron partially: the tetrahedron uses dark magic to self-cure if you erase less than N segments, and so it's the same as not erasing any segment). Also, to protect yourself from the tetraheldral curse,