def assert_equal(x, y)
  raise [x, y].inspect unless x == y
end

class Solution
  def self.run(n)
    f(n + 1)
  end

  def self.f(n)
    n <= 1 ? n : f(n - 1) + f(n - 2)
  end
end

=begin
  --
    |
     --
       |
        --
          |
           --
             |

1: 1, 1, 1, 1
2: 1, 1, 2
3: 1, 2, 1
4: 2, 1, 1
5: 2, 2
=end

assert_equal(5, Solution.run(4))
assert_equal(8, Solution.run(5))
puts "Yay!"