[EIP-155]Why did define the formula of v especially "35" or "36"

I understood the EIP-155 but I'm curious as to how you arrived at this formula.

v = CHAIN_ID * 2 + 35 or v = CHAIN_ID * 2 + 36

This is especially about the numbers 35 and 36. (I don't even know the origin of 27 and 28 in the previous definition formula.)