#include<bits/stdc++.h>
using namespace std;
struct qq
{
	int x,y,z;
};
 bool cmp(qq x,qq y)
{
  return x.z<=y.z;
  
  }

int main() 
{
	int n,i,j;
	struct qq a[50001];
	double s=0;
	scanf("%d",&n);
	for(i=2;i<=n;i++)
	{
		scanf("%d%d%d",&a[i].x,&a[i].y,&a[i].z );
	}
	sort(a+1,a+n+1,cmp);
	for(i=1;i<=n;i++)
	 s+=sqrt((a[i-1].x-a[i].x)*(a[i-1].x-a[i].x)+(a[i-1].y-a[i].y)*(a[i-1].y-a[i].y)+(a[i-1].z-a[i].z)*(a[i-1].z-a[i].z));
	printf("%.3lf",s);
	return 0;
	
}