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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def Append(self, value, timestamp):
 """Adds value at timestamp. Values must be added in order of increasing timestamp. Args: value: An observed value. timestamp: The timestamp at which value was observed. Raises: RuntimeError: If timestamp is smaller than the previous timstamp. """


    timestamp = self._NormalizeTime(timestamp)
    if self.data and timestamp < self.data[-1][1]:
      raise RuntimeError("Next timestamp must be larger.")
    self.data.append([value, timestamp])