HMIC 2016 Problem 2

Let $A B C$ be an acute triangle with circumcenter $O$, orthocenter $H$, and circumcircle $\Omega$. Let $M$ be the midpoint of $A H$ and $N$ the midpoint of $B H$. Assume the points $M, N, O, H$ are distinct and lie on a circle $\omega$. Prove that the circles $\omega$ and $\Omega$ are internally tangent to each other.