# Many digits

Let $x = \underbrace {444 ... 4} _ \text {2020 pieces}$, $y = - \underbrace {111 ... 1} _ \text {2020 pieces}$, $z =\underbrace { 222 ... 2} _ \text {2020 pieces}$. Find the sum of the digits of $x ^ 2 + 2xy + 2yz-z ^ 2-y$ in decimal.