Given an=an−1+an−2a_n = a_{n-1} + a_{n-2}an=an−1+an−2, if a1=1a_1=1a1=1 and a2=1a_2=1a2=1, what is a4a_4a4?
a4=2a_4 = 2a4=2
a4=3a_4 = 3a4=3
a4=4a_4 = 4a4=4
a4=5a_4 = 5a4=5