def get_checksum mtk_msg
    matchdata = /^\$(.+)\*/.match(mtk_msg)
    result = 0x00
    matchdata[1].chars.each do |c|
        result ^= c.ord
    end

    result
end

#
# assert_equal(31, get_checksum('$PMTK605*'))
# assert_equal(4, get_checksum('$PMTK226,3,30*'))


loop do
    result = get_checksum(gets)
    puts "#{result} \t 0x#{result.to_s(16)}"
end