hdu1143

3*N 的矩阵可以由 1*2 的小矩阵组成，问你有多少种情况。

/**/
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cctype>
#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <stack>
#include <queue>

typedef long long LL;
using namespace std;

LL f[35];

int main()
{
	//freopen("in.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);

	f[0] = 1;
	f[2] = 3;
	for (int i = 4; i <= 30; i += 2){
		f[i] = 4 * f[i - 2] - f[i - 4];
	}
	int n;
	while(scanf("%d", &n) == 1){
		if(n == -1) break;
		printf("%lld\n", f[n]);
	}

	return 0;
}
/**/