CN-SMO 2009 Problem 5

Let $X=(x_1,x_2,......,x_9)$ be a permutation of the set $\{1,2,\ldots,9\}$ and let $A$ be the set of all such $X$ . For any $X \in A$ , denote $f(X)=x_1+2x_2+\cdots+9x_9$ and $M=\{f(X)|X \in A \}$ . Find $|M|$ . ( $|S|$ denotes number of members of the set $S$ .)