title: Stop receiving messages after receiving a particular message from observable
body: <p>Observable emits values like 1,1,3,3,2,2,3,3,3,.. 4...,5,6..</p>
  <p>How could I stop receiving messages after receiving a particular element 4, Observable should stop consuming next element onwards.</p>
  <p>Thanks in advance for help.</p>
  <p>order of the messages are not same.</p>