IF THEN formula to calculate days worked

I want to create an if then formula. I have a spreadsheet that shows projects done by certain employees. If A1 is the person's initials B1 is the start date and C1 is the end date. I want a column that calculates the days it took to complete the route (minus weekends). However employee Eric S (initials ES) works 5 days a week (monday-friday) and Mike W (MW) works 4 days a week (Monday-Thursday) so they would use different formulas.
Mike W's formula would be:
SUM(INT((WEEKDAY(B1-{2,3,4,5})+C1-B1)/7))
Eric S's formula would be:
SUM(INT((WEEKDAY(B1-{2,3,4,5,6})+C1-B1)/7))

is there a way to write and IF THEN forumula to use Mike's forumla if A1 = MW and to use Eric's if A1 = ES ?