Is f(x) integrable on the interval -1 < x < 1?

[Swamifez]

Let

f(x)=

{1 if -1 < x<0;
{-1 if 0 < x < 1.

Prove that f(x) is integrable on -1 < x < 1.

 

[quasar987]

Just show that the superior and inferior integrals are equal.