Hermite Polynomial

Problem Background

Special for beginners, ^_^

Problem Description

Use a recursive method to compute the value of the Hermite polynomial:

$$h_n(x)=\begin{cases}1, &n=0\\2x,&n=1\\2xh_{n-1}(x)-2(n-1)h_{n-2}(x),&n>1\end{cases}$$

For given $x$ and positive integer $n$, both not exceeding $10$, compute the value of the polynomial.

Input Format

The given $n$ and positive integer $x$.

Output Format

Output the value of the polynomial, formatted to two decimal places (e.g. 4.00).

Sample Input

1 2

Sample Output

4.00

Constraints

Time limit: 1s, memory limit: 1024KiB for each test case.