import bisect
import copy
import decimal
import fractions
import heapq
import itertools
import math
import random
import sys
from collections import deque,defaultdict
from functools import lru_cache,reduce
from heapq import heappush,heappop,heapify,_heappop_max,_heapify_max
def _heappush_max(heap,item):
    heap.append(item)
    heapq._siftdown_max(heap,0,len(heap)-1)
from math import gcd as Gcd
read=sys.stdin.read
readline=sys.stdin.readline
readlines=sys.stdin.readlines

N=int(readline())
A=[4,3]
for _ in range(100):
    A.append(19*A[-1]/4-3*A[-2])
ans=A[N]
print('{:.10f}'.format(ans))