Your Python program will take an integer $(1-25),$ and an input string message from the user and encode it using a simple substitution cipher.

Each letter in the message will be replaced with the letter that comes n positions later in the alphabet. For example, for n $==3,\text{'}$a$\text{'}$ will be replaced with $\text{'}$d$\text{'},\text{'}$b$\text{'}$ with $\text{'}$e$\text{'},\text{'}$c$\text{'}$ with $\text{'}$f$\text{'},\text{'}$x$\text{'}$ with $\text{'}$a$\text{'},\text{'}$y$\text{'}$ with $\text{'}$b$\text{'},$ and so on$.$ The program should handle both uppercase and lowercase letters as well as numbers. Any characters that are not alphanumeric letters $($such as spaces, punctuation, etc.$)$ should remain unchanged.