Central bank sources say they're having problems with Indian currency: the bank is wondering what to do with all the Indian Rupees it holds, and the Indian currency that is in circulation and hidden away under the mattresses of Nepalis. Indian currency circulates openly not only in border townships but also in major urban centres in the inner hills. Commercial banks shy away from buying IRs because re-exchanging it at the Nepal Rastra Bank (NRB) can take up to three months. Sources at currency exchange counters, who are required to ask customers why they're buying or selling IRs, say people either want to keep cash in Indian currency or are selling money they "had at home." The NRB holds about Rs 20 billion in Indian rupees, of which Rs 4 billion is invested in Indian treasury bills, and another Rs 500 million with the Reserve Bank of India under a stand-by agreement for trading. Even government institutions like customs and hospitals accept the currency, and sources say it is impossible to gauge how much Indian currency is actually circulating