At the centre of a half ring of radius R =10 cm and linear charge density 4 nC m^-1, the potential is x π V. The value of x is ____.

At the centre of a half ring of radius $\displaystyle \mathrm{R}=10 \mathrm{~cm}$ and linear charge density $\displaystyle 4 \mathrm{nC} \mathrm{m}^{-1}$, the potential is $\displaystyle x \pi V$. The value of $\displaystyle x$ is $\displaystyle \_\_\_\_$.