A charge +q is fixed at each of the points x=x0x=3x0,x=5x0……∞ on the x - axis and a charge-q is fixed at each of the points x=2x0,x=4x0,x=6x0……∞. Here x0 is a positive constant. Take the electric potential at a point due to a charge Q at a distance r from it to be Q4π∈0r. Then the potential at the origin due to the above system of charges is