from decimal import Decimal

n = int(input())
if n == 0:
    print(4)
    exit()
dp = [Decimal(4), Decimal(3)] + [0] * (n - 1)
for i in range(2, n + 1):
    dp[i] = 19 * dp[i - 1] - 12 * dp[i - 2]
    dp[i] /= Decimal(4)
print(dp[n])