AS Level to Alevel grade contrbution

As a result of Covid-19 I no longer get to sit my AS level exams, therefore I may be awarded my target grade for Maths which is a C . However, at the end of A level I would like to have attained a B grade in maths overall. I would like to know if this is still possible giving that I may receive a C at AS level , if it is possible how well would I need to do in my A level exams ?
I am doing my A levels with the exam board CCEA.