n=int(input())
i=1
j=2
a=0
b=0
while i<=n:
    a+=1/i
    i+=1
while j<=n:
    b+=1/j
    j+=2
print('{:.4f}'.format(a-2*b))
/**************************************************************
	Problem: 1521
	User: admin
	Language: Python
	Result: Accepted
	Time:101 ms
	Memory:34480 kb
****************************************************************/