tijie

#include <iostream>
#include <cstdio>
using namespace std;
long long a[15];
long long n, m;
long long f(long long n, long long x){
	if(a[n]) return a[n];
	a[n] = 2 * x * f(n - 1, x) - 2 * (n - 1) * f(n - 2, x);
	return a[n];
}

int main(){
	cin >> n >> m;
	a[0] = 1, a[1] = 2 * m;
	cout << f(n, m) << ".00";

	return 0;
}