public class Euler389 {
    static class Stats {
        double mean;
        double variance;

        Stats(double m, double v) {
            mean = m;
            variance = v;
        }
    }

    private static Stats uniformDieStats(int sides) {
        double s = sides;
        return new Stats((s + 1.0) / 2.0, (s * s - 1.0) / 12.0);
    }

    private static Stats transitionSum(Stats countStats, int sides) {
        Stats perDie = uniformDieStats(sides);
        double mean = perDie.mean * countStats.mean;
        double var = perDie.variance * countStats.mean + perDie.mean * perDie.mean * countStats.variance;
        return new Stats(mean, var);
    }

    public static String solve() {
        Stats s = uniformDieStats(4);
        s = transitionSum(s, 6);
        s = transitionSum(s, 8);
        s = transitionSum(s, 12);
        s = transitionSum(s, 20);
        return String.format("%.4f", s.variance).replace(',', '.');
    }

    public static void main(String[] args) {
        System.out.println(solve());
    }
}