Formula to find sum of unique values related to month chosen from dropdown

I'm trying to make a formula that will count the unique number of values within a specific month that is chosen from a dropdown. Basically there will be an input form where people enter a location number and the month they went, and then I want a summary section where you can choose which month to view, and it will add up the sum of the unique locations visited that month. I've made a small example in my attached file.

Using my attached file as reference, when I've selected January from the month dropdown in B1, I would want B3 to show "2", since there are 2 unique location values for January. Similarly, if I changed the month dropdown to February, I would want B3 to show "3", since there are 3 unique locations values for that month.

I was able to easily do something similar with the =SUMIF function when I was counting the total number of visits at each location, but I'm assuming for this I need =COUNTIF or =COUNTIFS and I just can't figure it out. Hopefully all the information needed is here and in the attached.

Thank you.

Microsoft 365

Works perfectly!

Thank you so much Pepe. I was trying to ask in Reddit for help with this but my posts kept being auto flagged as spam and deleted. I am very happy to have found this forum and will return if I need to.

Thanks again.