fibonacci :D, in ruby, trying to make it smaller and lighter

fibonacci.rb

def fibonacci(n)
  a = [1,1]
  (n-2).times{ a[a.index(a.min)] = a[0]+a[1]}
  a.max
end

fibonacci2.rb

def fibonacci(n, a = [1,1])
  (n-2).times{ a[a.index(a.min)] = a[0]+a[1]}
  a.max
end

fibonacci3.rb

def fibo_sum(a=[1,1])
  [a.max, a.max + a.min]
end

def fibonacci(n)
  (n-2).times{ a = fibo_sum(a)}.max
end

fibonacci4.rb

def fibonacci(n, a=[1,1])
  (n-2).times{ a = [a.max, a.max + a.min]}[1]
end

fibonacci5.rb

def fibonacci(n, a=[1,1]) # where n is the index of number of the fibonacci you want... 1=> 1, 2=> 1, 3 => 2...
  (n-2).times{ a.replace([a.max, a.max + a.min])}[1]
end

I want to make it in one line, yet readable (no ; )....

fibonacci1 good for starters....

saved a line in the second one, plus generalized for any seed on the fibonacci-like series

fibo3 => looks better,,, longer but... better....

fibo4,,, refactored.....

fibonacci5,,, easier on the garbage collector and less memory consumption thanks to replace

and avoided using max to select result because i think [1] is more efficient!