Given a integer N greater than zero.
How many sequences of 1's and 2's are there such that sum of the numbers in the sequence = N ?
(not necessary that every sequence must contain both 1 and 2 )
example :
for N = 2 ; 11,2 => ans = 2 sequences of 1's and 2's
for N = 3 ; 11,12,21 => ans = 3 sequences of 1's and 2's