A semi-annual government bond selling for R937, with a coupon of 5.7% has a YTM of 13.9%. The bond matures in 25 years, but can be called in 9 years at a call price of R1059. What value do you need to input into your calculator for "N" to calculate Yield to Call? Provide your answer, in years, as a whole number (no decimal places needed)