Can someone very simply explain to me how to compute the expected distance from the origin for a random walk in $1D, 2D$, and $3D$? I've seen several sources online stating that the expected distance is just $\sqrt{N}$ where $N$ is the number of time steps, but others say that the expected distance is $\sqrt{\frac{2N}{\pi}}$. Which one is it and is it the same regardless of dimension?

Thanks