title: How to close the android app on onBackPressed?
body: <p>I have three screens (activities).Let's say A,B,C.</p>
  
  <p>The screen transition is in the order A,B,C.</p>
  
  <p>I want to close the application once the user tap "back" button from the third screen (screen C).</p>
  
  <p>How to do it?</p>