A person 'P' borrowed some money from a friend who lends under a unique interest structure. For the first two years, the annual interest rate is 5%. For the following two years, the rate increases to 10% per annum, and for the next two years after that, the interest rate rises to 20% per annum. If 'P' borrowed the money for a total of 6 years and paid Rs. 11,51,245 as interest, with the interest compounded annually, what was the principal amount that 'P' borrowed?