Formula challenge - convert Y/N to days of week

A long-time reader sent me an interesting problem this past week. The goal is to end up with a text string like "MWF" for Monday, Wednesday, Friday. The problem is that the weekdays are input as yes/no abbreviations like "NYNYNYN" for "MWF". 

Challenge

What formula will translate the "N" and "Y" to weekday abbreviations as shown in the screenshot above?

The workbook is attached below. Post your answer in the comments.

Extra points for style and elegance, but workhorse solutions are fine, too :)

Assumptions

1. All inputs are 7 characters and contain only "Y" or "N"
2. Days are mapped Sunday through Saturday, SMTWTFS.