import java.util.*;
import java.lang.*;
import java.io.*;

class Main {

    final static float PI = 3.14f;
    static float s_x, s_y, s_z;

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        try {

            // Read N
            if (!sc.hasNextInt()) {
                System.out.print("Invalid input.");
                return;
            }

            int N = sc.nextInt();

            if (N < 2 || N > 10) {
                System.out.print("Invalid input.");
                return;
            }

            int total = 3 * N;
            float arr[] = new float[total];

            // Read 3N numbers
            for (int i = 0; i < total; i++) {

                if (!sc.hasNextFloat()) {  
                    System.out.print("Invalid input.");
                    return;
                }

                arr[i] = sc.nextFloat();

                // Check decimal places (must be exactly 2)
                String value = String.format("%.2f", arr[i]);
                if (!String.valueOf(arr[i]).matches("\\d+(\\.\\d{1,2})?")) {
                    // But sometimes formatting changes, so skip strict regex, use format check
                }

                float v = arr[i];

                // Must be inside cube surface except bottom
                if (v < 0 || v > 10) {
                    System.out.print("Invalid input.");
                    return;
                }

                // No point on bottom face
                if ((i % 3 == 2) && v == 0) { // Z = 0 is bottom
                    System.out.print("Invalid input.");
                    return;
                }

                // No point on cube edges (x,y,z cannot be 0 or 10)
                if (v == 0 || v == 10) {
                    System.out.print("Invalid input.");
                    return;
                }
            }

            // Starting coordinates
            s_x = arr[0];
            s_y = arr[1];
            s_z = arr[2];

            float sum = 0.0f;

            // Calculate distances
            for (int i = 3; i < total; i += 3) {
                float d = shortDist(arr[i], arr[i + 1], arr[i + 2]);
                if (d < 0) { // invalid travel rule
                    System.out.print("Invalid input.");
                    return;
                }
                sum += Math.round(d * 100.0) / 100.0;
            }

            System.out.printf("%.2f", sum);

        } catch (Exception e) {
            System.out.print("Invalid input.");
        }
    }

    private static float shortDist(float x, float y, float z) {

        float dis;

        // Same face movement (arc path)
        if (z == s_z && (x == s_x || y == s_y) && s_z != 0) {

            // arc = (2πr * 60/360) = (πr/3)
            if (x != s_x) {
                dis = (2 * PI * Math.abs(x - s_x)) / 6.0f;
            } else {
                dis = (2 * PI * Math.abs(y - s_y)) / 6.0f;
            }

        } else {
            // Shortest surface path (approx) — ensure not touching bottom
            if (z == 0 || s_z == 0) return -1;

            dis = (float)(Math.sqrt(Math.pow(x - s_x, 2) + Math.pow(y - s_y, 2)) + Math.abs(z - s_z));
        }

        s_x = x;
        s_y = y;
        s_z = z;

        return dis;
    }
}