import java.util.Scanner;

public class To10 {

public static void main(String[] args) {

Scanner scan = new Scanner(System.in);

int n = scan.nextInt();

int arr[][] = new int[n][3];

for(int i=0; i<n; i++){

arr[i][0] = scan.nextInt();

arr[i][1] = scan.nextInt();

arr[i][2] = scan.nextInt();

}

//每个村到0号的花费

double a[][] = new double [n][2];

for(int i =1;i<n;i++){

a[i][0] = Math.sqrt(((arr[0][0]-arr[i][0])*(arr[0][0]-arr[i][0])+

(arr[0][1]-arr[i][1])*(arr[0][1]-arr[i][1])))

+ (arr[0][2]-arr[i][2])*(arr[0][2]-arr[i][2]);

a[i][1] = i;

}

//对花费进行排序

for(int i =1;i<n-1;i++){

for(int j=i+1;j<n-1;j++){

if(a[i][0]>a[j][0]){

double b=a[i][0];

a[i][0]=a[j][0];

a[j][0]=b;

double c=a[i][1];

a[i][1]=a[j][1];

a[j][1]= c;

}

}

}

double hei[] = new double[n];

hei[1] = a[1][0];

double sum = hei[1];

for(int i =2;i<n-1;i++){

hei[i] = a[i][0];

for(int j=i-1;j>=1;j--){

int e = (int) a[i][1];

int  f= (int) a[j][1];

hei[i] = hei[i]<(Math.sqrt(((arr[e][0]-arr[f][0])*(arr[e][0]-arr[f][0])+

(arr[e][1]-arr[f][1])*(arr[e][1]-arr[f][1])))

+ (arr[e][2]-arr[f][2])*(arr[e][2]-arr[f][2]))?hei[i]:(Math.sqrt(((arr[e][0]-arr[f][0])*(arr[e][0]-arr[f][0])+

(arr[e][1]-arr[f][1])*(arr[e][1]-arr[f][1])))

+ (arr[e][2]-arr[f][2])*(arr[e][2]-arr[f][2]));

}

sum+=hei[i];

}

      int v= (int) (sum*100);

System.out.println((double)v/100);

}

}