Standard Deviation of Returns Help

Ok so I have 591 companies that I have broken out into quin-tiles (1-5). In Column "C" I have each companies 12 month forward return as of that date and then in column "D" I have the companies Quintile rank for that period. What I want to do is in Column "H" calculate the standard deviation of returns for each Quintile. Now usually I would just use STDEV.S, but I'm not sure how to get that formula to only pick up the individual companies returns in the specific quintiles. Any help would be much appreciated

Cheers!