A person is to count 4500 currency notes. Let \(a_{n}\) denote the number of notes he counts in the \(n^{\text{th}\text{~}}\) minute. If \(a_{1} = a_{2} = \ldots = a_{10} = 150\) and \(a_{10},a_{11},\ldots\) are in an A.P. with common difference -2 , then the time taken by him to count all notes is