The current density in a cylindrical wire of radius \( 4 \, \text{mm} \) is \( 4 \times 10^{6} \, \text{A m}^{-2} \). The current through the outer portion of the wire between radial distances \( \frac{R}{2} \) and \( R \) is __________ \( \pi \, \text{A} \).