And finally, let's move on to case four. So, if we have an ionizable side chain group, but it is neither basic nor acidic, so we're basically dealing with two cases. And these two cases are 15 and tyrosine. If the amino acids are 15 or tyrosine, to calculate our pi value, we have to determine what the middle PKA value is out of the three different PKA values. And then we take that middle value and we basically sum it with the terminal alpha carboxyl PK value and we divide that by two. So to see what we mean, let's take a look at the following example.