Log in and Sign up screens
<p>I have following Activities(imagine Pinterest app):</p>

<p><strong>WellcomeActivity</strong> with two buttons - Sign up and Log in</p>

<p><strong>LogInActivity</strong> you come here from WellcomeActivity</p>

<p><strong>SignUpActivity</strong> you come here from WellcomeActivity</p>

<p><strong>MainActivity</strong> - you come here after you either logged in or signed up.</p>

<p>When user signed up or logged in I call <code>finish()</code> in <code>LogInActivity</code> or <code>SignUpActivity</code> and start <code>MainActivity</code>. But <code>WellcomeActivity</code> remains in the stack, so when I press Back button I'm again in <code>WellcomeActivity</code>. </p>

<p>I can't call <code>finish()</code> in it when I start <code>LogInActivity</code> or <code>SignUpActivity</code>, because if user decides to go back, he will exit the app.</p>

<p>Now, how do I design Activity transitions to have that Pinterest-like logic?</p>
