import fractions
n = int(input())
a = [None] * max(2, n + 1)
a[0] = fractions.Fraction(4)
a[1] = fractions.Fraction(3)
for i in range(2,len(a)):
    a[i] = (19 * a[i-1] -  12 * a[i-2]) / 4
print(float(a[n]))