class Fixnum

# File lib/mc-fib.rb, line 3
def closest_fibonacci
  #find fib until
  fib = [0, 1]
  i = 1
  while fib[i] < self do
    fib[i+1] = fib[i] + fib[i-1]
    i += 1
  end
  fib[-2]
end