Posting its seventh straight day of losses, the Sensex at the Bombay Stock Exchange fell 54 points, or 0.3 percent, to close at a fresh four-month low of 18,681, on Monday, as investors booked profits ahead of the monthly expiry of the derivatives contracts. The Sensex has now lost almost 890 points in seven trading sessions. The Nifty at the National Stock Exchange dropped 18 points, or 0.3 percent, to 5,634.But stock markets in Japan, Hong Kong, Singapore and South Korea gained between 0.3 percent and 1.7 percent, after Cyprus reached an accord with creditors on an international bailout.