A convertible bond issued by firm Unilever has a coupon rate of 10% (interest paid annually), maturity of 15 years, price of $1,007.83, and par value of $1,000. The bond's conversion premium per share is $11.43 and income differential per share is $6.24. All rates are annualized assuming a periodicity of 1 (i.e. annual compounding). What is the premium payback period of BigRed's convertible bond?

(If your solution is 4.44 years then enter "4.44" as the answer. Precision is 0.01+/- 0.02.)