Problems
Sum of squares Cnk
Sum of squares Cnk
Given a non-negative integer $n$, find the sum of binomial coefficients
$$
(C_n^{0})^2 + (C_n^{1})^2 + (C_n^{2})^2 + ... + (C_n^{n})^2
$$
\InputFile
One non-negative integer $n\:(n \le 30)$.
\OutputFile
Print the value of the sum.
Input example #1
3
Output example #1
20