input: Write a python function to calculate the nth Fibonacci number using memoization.
  assert calculate_fibonacci(0) == 0
  assert calculate_fibonacci(1) == 1
  assert calculate_fibonacci(5) == 5
  assert calculate_fibonacci(10) == 55
output: def calculate_fibonacci(n, memo={0: 0, 1: 1}):
      if n not in memo:
          memo[n] = calculate_fibonacci(n-1, memo) + calculate_fibonacci(n-2, memo)
      return memo[n]