Ok, i found a mistake, but still don't get it right.
I write:
<r>=\frac{1}{\pi}\frac{z_{0}^{3}}{a_{0}^{3}}∫e^{\frac{-2Zr}{a_{0}}}r dr
Where the limits are from -∞ to ∞
Integrating i let U= r, du=1, dv= e^{\frac{-2Zr}{a_{0}}}, V=\frac{a_{0}}{-2Z}e^{\frac{-2Zr}{a_{0}}}
this...