Problem 3: Write a Python program that requests from the user to enter a string s and then identifies and prints to the screen the longest substring whose characters occur in alphabetical order. For example, ifs = 'azcbobobegghakl', then your program should print: Longest substring in alphabetical order is: beggh. In case ties occur, print the first substring. For example, ifs = 'abcbcd', then your program should print: Longest substring in alphabetical order is: abc