How many severe crime incidents were reported at coordinate 41.64820151, -87.54430496?
coordinates refers to latitude, longitude; severe crime refers to index_code = 'I'
SELECT SUM(CASE WHEN T1.longitude = '-87.54430496' THEN 1 ELSE 0 END) FROM Crime AS T1 INNER JOIN IUCR AS T2 ON T1.report_no = T2.iucr_no WHERE T2.index_code = 'I' AND T1.latitude = '41.64820251'