"""
こんなのが正解のはず無いが...
"""

def solve():
    N = int(input())

    if N == 0:
        print(4)
        return
    elif N == 1:
        print(3)
        return

    dp = [0] * (N + 1)
    dp[0] = 4
    dp[1] = 3
    for i in range(2, N + 1):
        dp[i] = 19 / 4 * dp[i - 1] - 3 * dp[i - 2]

    print('%.30f' % dp[N])


if __name__ == '__main__':
    solve()