60求助！！！

#include<bits/stdc++.h>
using namespace std;
unsigned long long s; 
void hnt(int n,char a,char b,char c){
	if(n<1){
		return;
	}
	hnt(n-1,a,c,b);
	s++;
	hnt(n-1,b,a,c);
}
int main()
{
	int n;
	cin>>n;
	hnt(n,'A','B','C');
	cout<<s;
	return 0;
}