from decimal import *
getcontext().prec = 100
N = int(input())
A = [Decimal(0)]*(101)
A[0] = Decimal(4)
A[1] = Decimal(3)
for i in range(2, N+1):
    A[i] = (19*A[i-1]-12*A[i-2])/4
print(A[N])