CF630I Parking Lot

停车场共有 $2n-2$ 个停车位。共有 $4$ 种品牌的汽车，每种汽车的数量都远大于停车位的数量。 该公司首席执行官认为，如果停车场有 **恰好** $n$ 个连续汽车的品牌相同，则停车场会更漂亮。 给定n的值，问有多少的方案使停车场满足条件。

一行，包含一个整数 $n$（$3\leq n\leq 30$）。

输出一个整数，即总方案数。

Let's denote car makes in the following way: A — Aston Martin, B — Bentley, M — Mercedes-Maybach, Z — Zaporozhets. For $ n=3 $ there are the following appropriate ways to fill the parking lot: AAAB AAAM AAAZ ABBB AMMM AZZZ BBBA BBBM BBBZ BAAA BMMM BZZZ MMMA MMMB MMMZ MAAA MBBB MZZZ ZZZA ZZZB ZZZM ZAAA ZBBB ZMMM Originally it was planned to grant sport cars of Ferrari, Lamborghini, Maserati and Bugatti makes but this idea was renounced because it is impossible to drive these cars having small road clearance on the worn-down roads of IT City.