Assume s is a string of numbers.
Write a program that prints the longest substring of s in which the numbers occur in descending order. For example, if s = '561984235870154755310', then your program should print
Longest substring in numeric descending order is: 755310
In the case of ties, print the first substring. For example, if s = '742951', then your program should print
Longest substring in numeric descending order is: 742