One by one your neurons are replaced by their digital counterpart as a nano-scale computer in-place, with equivalent functionality. After which neuron number are you no longer you? You remain conscious throughout the process, the process may last however long with pauses for sleep.
After the replacement is complete, one by one these neurons are switched off with their functionality offloaded to their clone instantiated in a computer. After which neuron number are you no longer you?
This mind upload thought experiment convinced me that as long as there are no sharp discontinuities in experience, it makes no sense to ask what happened to the you. It also carries the implication that you are not your brain, but rather the abstract dynamical system instantiated in it.