import java.util.Arrays;
import java.util.Scanner;

/**
 * Created By XuanRan on 2021/6/10
 */
public class P5143 {

    public static int N;
    public static double ans = 0;

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        N = input.nextInt();

        fly[] f = new fly[N+1];

        for (int i = 1; i <= N; i++) {
            f[i] = new fly(input.nextInt(),input.nextInt(),input.nextInt());
        }

        Arrays.sort(f,1,N);

        for (int i = 2; i <= N; i++) {
            ans += Math.sqrt((f[i].x - f[i-1].x) * (f[i].x - f[i-1].x) + (f[i].y - f[i-1].y) * (f[i].y - f[i-1].y) + (f[i].z - f[i-1].z) * (f[i].z - f[i-1].z));
        }

        System.out.println(String.format("%.3f",ans));



    }

}
class fly implements Comparable<fly>{

    int x,y,z;

    public fly(int x, int y, int z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }

    @Override
    public int compareTo(fly o) {
        return this.z - o.z;
    }
}

实在找不到问题在哪了，样例数据还不能下载。