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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 get_free_memory():
 """Return current free memory on the machine. Currently supported for Windows, Linux, MacOS. :returns: Free memory in MB unit :rtype: int """

    if 'win32' in sys.platform:
        # windows
        return get_free_memory_win()
    elif 'linux' in sys.platform:
        # linux
        return get_free_memory_linux()
    elif 'darwin' in sys.platform:
        # mac
        return get_free_memory_osx()