SELECT
 CASE
  WHEN EXISTS (SELECT 1 FROM Elevations WHERE value < 0)
   THEN 'Invalid Input'
  ELSE (SELECT COUNT(*)
   FROM(
        SELECT e1.idx,e1.value,
               MAX(e2.value)AS max_before
        FROM Elevations e1
        LEFT JOIN Elevationse e2
         ON e2.idx<e1.idx
         GROUP BY e1.idx,e1.value
         )AS t
    WHERE t.value > COALESCE(t.max_before,-999999)
   )
   END AS result;