for each input, there can only be one corresponding output
In other words, for each input of -13, there can be only one corresponding output such as -15 in this example.
Therefore the missing input cannot be -1, 0, 11, and 17, because those input values are already matching up with corresponding outputs.
The missing input can be -5 or 2, because neither of those is yet to be showing a corresponding output.
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