from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline
N = int(input())
B = [0]*(101)
B[0] = 4
B[1] = 12
for i in range(2,N+1):
    B[i] = 19*B[i-1] - 48*B[i-2]

ans = B[N]/pow(4,N)
print(ans)