Snowflake - Flatten nested JSON array

WITH str AS
(
SELECT '{
   "a":"a",
   "b":[
      {
         "c":"c1",
         "d":[
            1,
            2,
            3,
            4,
            5,
            6,
            7
         ]
      },
      {
         "c":"c2",
         "d":[
            10,
            20,
            30,
            40,
            50,
            60,
            70
         ]
      }
   ]
}' AS json_str),
obj as 
(
SELECT parse_json(json_str) as json_obj from str
),
l1 as (
SELECT 
json_obj:a::STRING as a,
VALUE:c::string as c,
VALUE:d as d_array
FROM obj, LATERAL FLATTEN(INPUT=> json_obj:b)
)
SELECT a, c, VALUE as d
FROM l1, LATERAL FLATTEN(INPUT => d_array);