SHARYGIN 2017 Problem 4

A triangle $ABC$ is given. Let $C'$ be the vertex of an isosceles triangle $ABC'$ with $\angle C' = 120^\circ$ constructed on the other side of $AB$ than $C$, and $B'$ be the vertex of an equilateral triangle $ACB'$ constructed on the same side of $AC$ as $ABC$. Let $K$ be the midpoint of $BB'$. Find the angles of triangle $KCC'$.