Define function $$$f(n)$$$ to be the number of different arrays $$$a$$$ of positive integers, such that the sum of the elements in array $$$a$$$ equals to $$$n$$$.
For example, $$$f(3)=4$$$, and the four different arrays are $$$\{1,1,1\},\{1,2\},\{2,1\},\{3\}$$$.
You are given a positive integer $$$k$$$. Please find the answer of $$$f(k)$$$.
There is only one line in the input containing a single integer $$$k\ (1\leq k\leq 20)$$$.
Print a single integer: the answer of $$$f(k)$$$.
3
4
4
8
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