def solve k, x
    dp = Array.new(k + 1, 0.0)
    (k - 1).downto(0){|i|
        tmp = 0.0
        1.upto(6){|j|
            if i + j > k
                tmp += x
            else
                tmp += dp[i + j]
            end
            }
        dp[i] = tmp / 6 + 1
        }
    return dp[0]
end

k = gets.to_i
ok = 0
ng = 1e9
100.times{
    mid = (ok + ng) / 2
    if solve(k, mid) >= mid 
        ok = mid
    else
        ng = mid
    end
    }
p ok