How can i have Validation rule thrown where i cannot edit from stage 6 to stage 1,2,3,4 , but i can edit from stage 6 to stage 1,2,3,4

Question

how to create a validation rule , where users cannot edit the stage from stage 6 to stage 1,2,3,4 in sfdc, but they can edit the stage from stage 1, 2, 3, 4, to stage -6 in sfdc

AND(
    OR(
        AND(
            ISPICKVAL(PRIORVALUE(StageName), "stage 6 – SellThru Into Hospital"),
            OR(
                ISPICKVAL(StageName, "Stage 1 - Qualified"),
                ISPICKVAL(StageName, "Stage 2 - Needs Identified & Accepted"),
                ISPICKVAL(StageName, "Stage 3 - Value/Solution Presented & Accepted"),
                ISPICKVAL(StageName, "Stage 4 - Specific Price / Budget Confirmed")
            )
            ),
            AND(
                ISPICKVAL(PRIORVALUE(StageName), "Stage 1 - Qualified"),
                ISPICKVAL(StageName, "stage 6 – SellThru Into Hospital"
            )
            ),
            AND(
                ISPICKVAL(PRIORVALUE(StageName), "Stage 2 - Needs Identified & Accepted"),
                ISPICKVAL(StageName, "stage 6 – SellThru Into Hospital"
            )
            ),
            AND(
                ISPICKVAL(PRIORVALUE(StageName), "Stage 3 - Value/Solution Presented & Accepted"),
                ISPICKVAL(StageName, "stage 6 – SellThru Into Hospital"
            )
            ),
            AND(
                ISPICKVAL(PRIORVALUE(StageName), "Stage 4 - Specific Price / Budget Confirmed"),
                ISPICKVAL(StageName, "stage 6 – SellThru Into Hospital"
            )
        )
    )
)