#2022/5/23 21:06
#1 1
#2 1+1/-2
#3 1+1/-2+1/3+1/-4
n=int(input())
sum1,sum2=0,0
for i in range(1,n+1):
    if i%2==0:
        sum1+=-(1/i)
    else:
        sum2+=1/i
print("{:.3f}".format(sum1+sum2))