from decimal import *

def main():
  getcontext().prec = 100
  
  n = int(input())
  a = [0 for _ in range(101)]
  
  a[0] = Decimal(4)
  a[1] = Decimal(3)

  for i in range(2, 101):
    a[i] = (Decimal(19) * a[i-1] - Decimal(12) * a[i-2]) / Decimal(4)

  print("{:.20f}".format(a[n]))
  

if __name__ == '__main__':
  main()