def f(dp,n)
	dp2=dp.size.times.map{0.0}
	dp.size.times{|i|
		break if n<=i
		if dp[i]>0
			(1..6).each{|j|
				dp2[i+j]+=dp[i]/6.0
			}
		end
	}
	return dp2
end
es=21.times.map{0.0}
(1..20).each{|i|
	dp=43.times.map{0.0}
	dp[0]=1.0
	ans=0
	arr=[]
	i.times{|k|
		dp=f(dp,i)
		dp.size.times{|j|
			ans+=(k+1)*dp[j] if j>=i
		}
	}
	es[i]=ans
}
puts es[gets.to_i]