Dynamically changing fields for calculating standard deviation

I don't think dynamic fields is the correct term for this based on my search results, but I don't know how else to describe it.
I have a sheet of different populations, and I'd like to calculate the standard deviation for each group in another column
So column A has a subject name, B has their score, and my output column C has a formula for standard deviation.
I need the range of the standard deviation to change dynamically with the subjects. Here's a sample file stdevsample.xlsx

Thanks for your help.

Thanks! Worked great!