So notice they both have negative charges. And that makes sense, because if both of these groups give the same type of charge, then to basically cancel out the positive charge, we have to average these two negative charges. And so we average these two PK values. So 4.1 plus 3.1, that gives us 7.2. We divide that by two, that gives us 3.6. So what that means is at a PH of 3.6, these two negative charges from these two groups will exactly cancel out this positive charge found on this terminal alpha amino group.