Determine whether the function f: [0,1] R given by:

f(x):=

3 if

1 if \

is Riemann integrable on [0,1].

I know that if it is Riemann integrable, sup L(P, f) = inf U(P,f), P being the partition of [0,1]

or (lower integral of f over [0,1]) = (upper integral of f over [0,1])

How do I show if it is or not?