Masses
\[
m,\ \left(\frac{1}{2}\right)\frac{1}{2}m,\ \left(\frac{1}{2}\right)^2\frac{1}{3}m,\ \ldots,\ \left(\frac{1}{2}\right)^{N-1}\frac{1}{N}m,\ \ldots \infty
\]
are placed at
\[
x=1,2,3,\ldots,N,\ldots \infty
\]
respectively. If the total mass is \(M\), then the centre of mass of the system is