#include<bits/stdc++.h>
using namespace std;

struct point {
	double x;
	double y;
	double z;
} a[50005];

bool cmp(point a,point b) {
	if(a.x!=b.x)return a.x>b.x;
	if(a.y!=b.y)return a.y>b.y;
	if(a.z!=b.z)return a.z>b.z;
}

int main() {
	int n;
	cin>>n;
	for(int i=1; i<=n; i++) {
		cin>>a[i].x>>a[i].y>>a[i].z;
	}
	sort(a+1,a+1+n,cmp);
	double sum=0;


	for(int i=2; i<=n; i++) {
		sum+=sqrt((double)
		          ((a[i].x)-(a[i-1].x))*((a[i].x)-(a[i-1].x))+
		          (double)((a[i].y)-(a[i-1].y))*((a[i].y)-(a[i-1].y))+
		          (double)((a[i].z)-(a[i-1].z))*((a[i].z)-(a[i-1].z))
		         );
	}

	printf("%.3lf",sum);

}