\[S_{кр} = 2\pi\]
\[S_{кр} = \pi r^{2} = 2\pi\]
\[r^{2} = 2\]
\[r = \sqrt{2}.\]
\[a_{кв} = 2r = 2 \cdot \sqrt{2} = 2\sqrt{2}.\]
\[Ответ:2\sqrt{2}.\]