import sys


def input(): return sys.stdin.readline().rstrip()


def main():
    A = [4, 3]
    N = int(input())
    for i in range(N-1):
        A.append((19*A[-1]-12*A[-2])/4)

    print(f'{A[N]:.12f}')


if __name__ == '__main__':
    main()