text: #!/usr/bin/env python
  
  
  def fib(n):
      """Calculate the n-th fibonacci number."""
      def acc_fib(n, n_m2=0, n_m1=1):
          for i in range(n):
              n_m2, n_m1 = n_m1, n_m1+n_m2
          return n_m2
      return acc_fib(n)
  
  print(len(str(fib(20000))))
  