Throw a dice-expected value.

Question

We throw the dice three times. Let $X_i$- number of throws, in which we get number $i$. Find expected value and variance random variable $Y=\sum_{i=1}^{6} (-1)^iX_i$. We know, that $X_i=0,1,2,3$. $E(Y)=E(-X_1+X_2-X_3+X_4-X_5+X_6)$. But $X_i$ are not independent. And I don't know what to do next.