The numbers of all offices in the new building of the Tax Office of IT City will have lucky numbers.

Lucky number is a number that consists of digits 7 and 8 only. Find the maximum number of offices in the new building of the Tax Office given that a door-plate can hold a number not longer than *n* digits.
The only line of input contains one integer *n* (1 ≤ *n* ≤ 55) — the maximum length of a number that a door-plate can hold.
none
2
6
1
2
3
14
5
62
12
8190
34
34359738366
43
17592186044414
49
1125899906842622
54
36028797018963966
55
72057594037927934
def re(a,n):
    global l
    global t
    if len(str(a))>n:
        return 
    if str(a).count("8")+str(a).count("7")==len(str(a)) and a not in l :
        l.append(a)
        t+=1
    re(a*10+7,n)
    re(a*10+8,n)
l=[]
t=0
n=int(input())
if n==1:
    print(2)
elif n==2:
    print(6)
else:
    t=6
    for i in range(2,n):
        t=(t*2)+2
    print(t)
