The formula for resistors linked in parallel is a little more complex. Given two resistors along with resistances R1 and R2 linked in parallel the equivalent resistance is given through the inverse of the sum of the inverses, i.e.

 1
 Requiv = --------
 1 1
 -- + --
 R1 R2
If there are more than two resistors you continue to invert the sum of their inverses; e.g. for four resistors you have:
1
Requiv = ------------------
1 1 1 1
-- + -- + -- + --
R1 R2 R3 R4

Write a program that calculates the resistance of a a group of resistors arranged in parallel. The resistances will all be passed as command line arguments.