Tax Season! I was employed for a period from x until y in a year and I get pay check of amount z on every alternate Friday of the week starting from first Friday since I am employed. Help me find out how much did I earn during my employment period.

Example

 x = 01-Jan-2014
 y = 14-Feb-2014
 z = $2000 (x will always be <y)

This period has total 4 alternate Fridays which were my "pay-days", so the salary for this period was 4*2000 = %8000