from decimal import Decimal

n = int(input())
A = [0 for _ in range(n + 1)]

if n == 0:
    print(4.0)
    exit()
if n == 1:
    print(3.0)
    exit()

A[0] = Decimal(4.0)
A[1] = Decimal(3.0)
for i in range(2, n + 1):
    A[i] = Decimal(19 / 4) * A[i - 1] - 3 * A[i - 2]
print(A[n])