input: def findMaxValue(nested_dict):
      """
      Find the maximum value within a nested dictionary.
      >>> findMaxValue({"key1": {"value1": 10, "value2": 20}, "key2": {"value3": 40}})
      40
      >>> findMaxValue({"level1": {"level2": {"level3": 15}, "level2b": 25}})
      25
      """
output:     max_value = float('-inf')
      for key, value in nested_dict.items():
          if isinstance(value, dict):
              max_value = max(max_value, findMaxValue(value))
          else:
              max_value = max(max_value, value)
      return max_value