哦

#include <bits/stdc++.h>
using namespace std;
long long a[100001];
int n;
 
int main()
{
	cin>>n;
	a[1]=0,a[2]=6;
	a[3]=6;
	for(int i=4;i<=n;++i)
	{
		a[i] = a[i-1]+2*a[i-2];
	
	}
	cout<<a[n];
	return 0;

}