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Problems

Sum of squares Cnk

Sum of squares Cnk

Time limit 1 second
Memory limit 128 MiB

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

Input data

One non-negative integer n\:(n \le 30).

Output data

Print the value of the sum.

Examples

Input example #1
3
Output example #1
20