The current density in a cylindrical wire of radius \( r = 4.0 \,\text{mm} \) is \( 1.0 \times 10^{6} \,\text{A}/\text{m}^{2} \). The current through the outer portion of the wire between radial distances \( \frac{r}{2} \) and \( r \) is \( x \pi \,\text{A} \); where \( x \) is ________.