def fib(n):
    f = ((1 + 5**0.5) / 2)**n / 5**0.5 + 0.5
    return int(f)
N = int(input())
L = []
for i in range(N) :
    l = fib(i+1)**2
    L.append(l)
print(sum(L))
#print(L)