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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 setup(job, input_file_id, n, down_checkpoints):
 """Sets up the sort. Returns the FileID of the sorted file """

    # Write the input file to the file store
    job.fileStore.logToMaster("Starting the merge sort")
    return job.addChildJobFn(down,
                             input_file_id, n,
                             down_checkpoints=down_checkpoints,
                             memory='600M').rv()