Ram Prashad is admitted to Guru Teg Bahadur Hospital with respiratory infection for which antibiotic tobramycin is ordered. The clearance and Vd of tobramycin in him are 160 ml/min and 40 L, respectively. If you wish to give Ram Prashad an intravenous loading dose to achieve the therapeutic plasma concentration of 4 mg/L rapidly, how much should be given?