Lattice angles of lattice polygons

This paper is dedicated to a lattice analog to the classical ``sum of interior angles of a polygon theorem''. In 2008, the first formula expressing conditions on the geometric continued fractions for lattice angles of triangles was derived, while the cases of $n$-gons for $n > 3$ remained unresolved. In this paper, we provide the complete solution for all integer $n$. The main results are based on recent advances in geometry of continued fractions.