I - Tri Tiling

 

Time Limit:1000MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u

Submit Status

#include<cstdio>
using namespace std;
int f(int n)
{
    if(n==0)
        return 1;
    if(n==2)
        return 3;
    else
        return 4*f(n-2)-f(n-4);
}
int main()
{
    int n;
    while(scanf("%d",&n)==1&&n!=-1)
        if(n%2==0)
        printf("%d\n",f(n));
        else
        printf("%d\n",0);
    return 0;
}

 

Description

In how many ways can you tile a 3xn rectangle with 2x1 dominoes?  Here is a sample tiling of a 3x12 rectangle. 

Input

Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer 0 <= n <= 30.

Output

For each test case, output one integer number giving the number of possible tilings.

Sample Input

2
8
12
-1

Sample Output

3
153
2131



DP!