import sys

sys.setrecursionlimit(10 ** 6)
# from itertools import *
from bisect import *
# from math import *
from collections import *
from heapq import *
from random import *
from decimal import *
import numpy as np

int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def MI1(): return map(int1, sys.stdin.readline().split())
def MF(): return map(float, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LF(): return list(map(float, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
dij = [(0, 1), (1, 0), (0, -1), (-1, 0)]

def main():
    n=II()
    d4=Decimal(4)
    d3=Decimal(3)
    aa=[d4,d3]
    for _ in range(n-1):
        aa.append((19*aa[-1]-12*aa[-2])/4)
    print(aa[n])

main()