import java.util.Locale;

public class Euler607 {
    public static String solve() {
        double AtoB = 100.0;
        double rt2 = Math.sqrt(2.0);

        double d0 = 25.0 * (rt2 - 1.0);
        double[] dv = { d0, 10.0, 10.0, 10.0, 10.0, 10.0, d0 };
        double[] sp = { 10.0, 9.0, 8.0, 7.0, 6.0, 5.0, 10.0 };

        double U = AtoB / rt2;

        double lo = 0.0, hi = 0.1;
        for (int it = 0; it < 200; it++) {
            double mid = (lo + hi) / 2.0;
            double s = 0.0;
            for (int i = 0; i < 7; i++) {
                double t = mid * sp[i];
                double c = Math.sqrt(1.0 - t * t);
                s += dv[i] * t / c;
            }
            if (s < U) {
                lo = mid;
            } else {
                hi = mid;
            }
        }

        double mid = (lo + hi) / 2.0;
        double ans = 0.0;
        for (int i = 0; i < 7; i++) {
            double t = mid * sp[i];
            double c = Math.sqrt(1.0 - t * t);
            ans += dv[i] / (sp[i] * c);
        }

        return String.format(Locale.US, "%.10f", ans);
    }

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