  It is known that the spectral type of the almost Mathieu operator depends in
a fundamental way on both the strength of the coupling constant and the
arithmetic properties of the frequency. We study the competition between those
factors and locate the point where the phase transition from singular
continuous spectrum to pure point spectrum takes place, which solves
Jitomirskaya's conjecture in \cite{Ji95,J07}. Together with \cite{Aab}, we give
the sharp description of phase transitions for the almost Mathieu operator.
