Who lives........

Puzzle:
King makes 1000 soldiers of a defeated army stand in a circle.
He numbers them 1 to 1000.
Starting from 1st soldier, he beheads every alternate soldier till last soldier is left, whom he sets free.
If u were one of those soldiers & given an option to choose number, what number will you be standing at?
(i.e. what is the number of soldier set free?)

Additional: Provide a general formula for any number (N) of soldiers.