So I don't really understand integrals as much as I had hoped... can someone help me figure out this really simple problem?

Find the lower and upper integrals of $\displaystyle \int_0^1 f(x) dx $ if f : [0,1] $\displaystyle \rightarrow$ R is given by

f(x):=

x if x $\displaystyle \in$ Q $\displaystyle \cap$ [0,1]

-x if x $\displaystyle \in$ (R \ Q) $\displaystyle \cap$ [0,1]