$memo = Array.new(100, 0.0)
def E(x)
    return $memo[x] if $memo[x] > 0.0
    return 0.0 if x >= $k
    res = 1.0
    6.times do |i|
        res += E(x + i + 1) / 6.0
    end
    return $memo[x] = res
end
$k = gets.to_i
puts E(0)