import sys sys.setrecursionlimit(10 ** 6) # from itertools import * from bisect import * # from math import * from collections import * from heapq import * from random import * from decimal import * import numpy as np int1 = lambda x: int(x) - 1 p2D = lambda x: print(*x, sep="\n") def II(): return int(sys.stdin.readline()) def MI(): return map(int, sys.stdin.readline().split()) def MI1(): return map(int1, sys.stdin.readline().split()) def MF(): return map(float, sys.stdin.readline().split()) def LI(): return list(map(int, sys.stdin.readline().split())) def LI1(): return list(map(int1, sys.stdin.readline().split())) def LF(): return list(map(float, sys.stdin.readline().split())) def LLI(rows_number): return [LI() for _ in range(rows_number)] dij = [(0, 1), (1, 0), (0, -1), (-1, 0)] def main(): n=II() d4=Decimal(4) d3=Decimal(3) aa=[d4,d3] for _ in range(n-1): aa.append((19*aa[-1]-12*aa[-2])/4) print(aa[n]) main()