The structure of a peptide is given below.

If the absolute values of the net charge of the peptide at pH = 2, pH = 6, and pH = 11 are $$\mid 𝑧_1 \mid, \mid 𝑧_2 \mid$$, and $$\mid 𝑧_3 \mid$$, respectively, then what is $$\mid 𝑧_1 \mid + \mid 𝑧_2 \mid + \mid 𝑧_3 \mid$$?