#include<bits/stdc++.h>
using namespace std;
double x[50005],y[50005],z[50005];
int main(){
	double n;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>x[i]>>y[i]>>z[i];
	}
	for(int i=1;i<=n;i++){
		for(int o=1;o<=n-1;o++){
			if(z[o]>z[o+1]){
				swap(z[o],z[o+1]);
				swap(y[o],y[o+1]);
				swap(x[o],x[o+1]);
			}
		}
	}
	double ans=0;
	for(int i=1;i<=n-1;i++){
		ans+=sqrt((x[i+1]-x[i])*(x[i+1]-x[i])+(y[i+1]-y[i])*(y[i+1]-y[i])+(z[i+1]-z[i])*(z[i+1]-z[i]));
	}
	printf("%.3lf",ans);
//	
//	
//	cout<<endl;
//	for(int i=1;i<=n;i++){
//		cout<<x[i]<<" "<<y[i]<<" "<<z[i]<<endl;
//	}
//	
//	
	return 0;
}