XSS Challenge #3

Welcome to my third XSS challenge!
This Challenge is the "difficult version" of XSS Challenge #1
The only difference between XSS Challenge #1 that XSS Challenge #3 has X-Frame-Options set to Deny, while XSS Challenge #1 is not.
This challenge's goal is to execute an alert() on this page, by following the rules.

Rules

The payload has to be working on a modern browser.

Link

http://secbot.me/xss-challenges/xss-challenge3.php?xss=[Payload]

Note: X-Frame-Options has been set to Deny, to make the challenge more realistic to live web-applications.

Solvers

Oliver Skånberg: The first person to solve this challenge, after having this challenge running for two years!. Click to view solution