# coding: utf-8
import array, bisect, collections, copy, heapq, itertools, math, random, re, string, sys, time
from decimal import *
sys.setrecursionlimit(10 ** 7)
INF = 10 ** 20
MOD = 10 ** 9 + 7


def II(): return int(input())
def ILI(): return list(map(int, input().split()))
def IAI(LINE): return [ILI() for __ in range(LINE)]
def IDI(): return {key: value for key, value in ILI()}


def read():
    N = II()
    return N


def solve(N):
    dp = [decimal(0)] * 101
    dp[0] = decimal(4)
    dp[1] = decimal(3)
    for i in range(2, N + 1):
        dp[i] = (dp[i - 1] * 19 - dp[i - 2] * 12) / 4

    ans = dp[N]

    return ans


def main():
    params = read()
    print(solve(params))


if __name__ == "__main__":
    main()