कौन सा महाजनपद उत्तर प्रदेश के आधुनिक कुशीनगर और देवरिया जिलों के आस-पास स्थित था?

In Ancient Indian Statecraft, Kautilya's 'Rajamandala' theory primarily deals with:

The First Buddhist Council was held at ______.

Which ancient Indian text contains references indicating that population counts or census-like records were maintained in ancient India?