text: class Solution1:
      def fib(self, n: int) -> int:
          return n if n < 2 else self.fib(n-1) + self.fib(n-2)
  
  
  class Solution2:
      def fib(self, n):
          if n < 2:
              return n
          prev = [0, 1]
          while n >= 2:
              prev[0], prev[1] = prev[1], prev[0] + prev[1]
              n -= 1
          return prev[1]
  