Test 1
Given an integer n return the nth number in Fibonacci sequence. Fibonacci sequence are 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ... where each number is the sum of the two preceding ones. More information about Fibonacci sequence can be found here.
fibonacci(2) -> 1
fibonacci(5) -> 3
fibonacci(7) -> 8