Arrange the following in increasing order of their crystal field splitting energy

I. $\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$

II. $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$

III. $\left[\mathrm{Co}(\mathrm{CN})_{6}\right]^{3-}$

IV. $\left[\mathrm{CoF}_{6}\right]^{3-}$