杭电Hd 2047 阿牛的EOF牛肉串

import java.util.Scanner;
//考虑角度要定在末尾位置
//如果末尾是E或F,则种数为2*a(i-1);如果末尾是O,则末2位一定是EO或FO,则种数为2*a(i-2)
public class Hd2047 {
 public static void main(String[] args) {
  Scanner sc = new Scanner(System.in);
  while (sc.hasNext()) {
   int n = sc.nextInt();
   long[] a = new long[40]; //注意类型越界
   a[1] = 3;
   a[2] = 8;
   if (n >= 3) {
    for (int i = 3; i < 40; i++) {
     a[i] = 2 * a[i - 1] + 2 * a[i - 2];
    }
   }
   System.out.println(a[n]);
  }
 }

}