def feiBo(n):
    if n == 1 or n == 2 :
        return 1
    else:
        return feiBo(n - 1) + feiBo(n - 2);
n = int(input())
s = 0
for i in range (1,n+1):
     s += feiBo(i) / feiBo(i + 1)
print('%.3f' % s)                

/**************************************************************
	Problem: 1147
	User: admin
	Language: Python
	Result: Accepted
	Time:98 ms
	Memory:34480 kb
****************************************************************/