<image> It is a great creation in our ancient masterpiece "The Nine Chapters on the Mathematical Art" to use "mutual subtraction method" to find the greatest common divisor of two positive integers. This great creation is essentially the same as the ancient Greek algorithm - the "Euclidean algorithm". The program flowchart shown in the figure is derived from the "Euclidean algorithm". When the inputs are a=288 and b=123, the output a=______.