Where to put logout in an Android app?

I have an app that relies on a particular web service. It can't be used without login in, so the first screen users see is the login screen. Until recently I didn't thought that users would ever want to log out, but indeed that can happen in rare cases.

QUESTION: Where is the most intuitive place to put logout?

• Button in the left menu?
• In the preferences? (even though it can't really be called a preference)
• In Accounts, in the general Android settings?