def format_time(decisecond):
    """
    Convert time in tenths of seconds
    into formatted string m:ss.t

    :param decisecond: int >= 0

    :return: str
    """
    assert isinstance(decisecond, int)
    assert decisecond >= 0

    decisecond, tenths = decisecond//10, decisecond % 10
    minutes, seconds = decisecond//60, decisecond % 60

    return '%d:%02d.%d' % (minutes, seconds, tenths)