The Pell sequence is the sequence of integers defined by the initial values
P(0) = 0, P(1) = 1
and the recurrence relation
P(n) = 2 * P(n-1) + P(n-2)
The first few values of P(n) are
0, 1, 2, 5, 12, 29, 70, 169, 408, 985, 2378, 5741, 13860, 33461, 80782, 195025, 470832, ...
Your task is to write a method that returns nth Pell number