from decimal import *

N = int(input())
if N == 0:
    print(4)
elif N == 1:
    print(3)
else:
    a0, a1 = Decimal(4), Decimal(3)
    getcontext().prec = 100
    for i in range(N - 1):
        a2 = (a1 * 19 - 12 * a0)/4
        a1, a0 = a2, a1
    print(a2)