Tax on debenture interest

I purchase a debenture of face value of 1000 with a coupon rate of 12% pa and interest payment ( Rs 120 ) to be made on 1st Oct every year .The debentures were issued by the company in Sept 2011 for a tenor of 5 years. I purchase this on 1 Feb 2013 for Rs 1015 from secondary market on a stock exchange. I will receive my first interest payment of Rs 120 on 01/10/2013. What is my accrued interest I need to offer for tax in FY 2012-13, i.e Fin Year ending on 31/03/2013?  Please also show the basis of calculations.