n=int(input())
rr=[0.0]*(n+3)
rr[1]=1.0
rr[2]=5/2.0
for i in range(3,n+1,1):
	for x in range(i):
		rr[i]+=(rr[x]+rr[i-x-1])/i
print("%.11f" % (rr[n]))