How to get index from a key when using JsonFlattener.flattenAsMap?

Question

Keys from Map are printed as [index].keyname. How to get the index value from keys?

Code:

Map<String, Object> flattenedJsonMap = JsonFlattener.flattenAsMap(response.readEntity(String.class));

Map<String,Object> keysMap = new HashMap<>();
flattenedJsonMap.forEach(
       (k, v) -> keysMap.put(k, v)
);

for (String kval : keysMap.keySet()) {
    if (kval.contains("paper_id")) {
           System.out.println("\nkval="+kval+"\n"+keysMap.get(kval));
    }
}

Sample output

kval=[3].paper_id
01e3b313e78a352593be2ff64927192af66619b5

kval=[1].paper_id
004f0f8bb66cf446678dc13cf2701feec4f36d76

kval=[2].paper_id
01d162d7fae6aaba8e6e60e563ef4c2fca7b0e18

Wanted to get the total or get the index values (1,2,3 etc) from key ([1].paper_id)