Fly height mode

You like tracking airplane flights a lot. Specifically, you maintain history of an airplane’s flight at several instants and record them in your notebook. Today, you have recorded N such records h1, h2, ..., hN, denoting the heights of some airplane at several instants. These records mean that airplane was first flying on height h1, then started changing its height to h2, then from h2 to h3 and so