import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

# B[k] = 4^kA_k とすると、全部整数で計算できる

N = int(read())

B = [4,12] + [0] * 100
for k in range(2,101):
    B[k] = 19 * B[k-1] - 48 * B[k-2]

A = [x / (4 ** i) for i,x in enumerate(B)]

A[0], A[4]

answer = A[N]
print('{:.20f}'.format(answer))