ROT13 is a Caesar cipher that shifts every English letter forward by 13 places.
For example, encrypting "Programming Online Judge" with ROT13 gives "Cebtenzzvat Bayvar Whqtr". Applying ROT13 once more to an encrypted string restores the original text, so "Cebtenzzvat Bayvar Whqtr" turns back into "Programming Online Judge".
ROT13 applies only to uppercase and lowercase English letters. Any character that is not a letter stays exactly as it is. For example, encrypting "One is 1" with ROT13 gives "Bar vf 1".
Given a string, write a program that encrypts it with ROT13 and prints the result.