Using extrabucks towards a "spend $20 get $5 ECB" at CVS?

There is currently a "spend $20 get $5 ECB" on Cetaphil products at Walgreens. Can I buy something that is $20, and then use a $15 ECB to pay for that, and still get the $5 ECB?

Or is it like Walgreens Cash promotions where the amount paid for using Walgreens Cash won't count towards the spend requirement?

Thank you!