import sys
import decimal


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


def main():
    decimal.getcontext().prec = 100
    A = [decimal.Decimal(4), decimal.Decimal(3)]
    N = int(input())
    for i in range(N-1):
        A.append((19*A[-1]-12*A[-2])/4)

    print(A[N])


if __name__ == '__main__':
    main()