title: Longest substring in alphabetical order
body: <p>Write a program that prints the longest substring of s in which the letters occur in alphabetical order. For example, if s = 'azcbobobegghakl', then your program should print</p>
  
  <p>Longest substring in alphabetical order is: beggh</p>
  
  <p>In the case of ties, print the first substring. For example, if s = 'abcbcd', then your program should print</p>
  
  <p>Longest substring in alphabetical order is: abc</p>