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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 estimate(self, upgrades):
 """Estimate the time needed to apply upgrades. If an upgrades does not specify and estimate it is assumed to be in the order of 1 second. :param upgrades: List of upgrades sorted in topological order. """

        val = 0
        for u in upgrades:
            val += u.estimate()
        return val