#include<bits/stdc++.h>
using namespace std;
struct dian{
	int x;
	int y;
	int z;
}a[1001];
bool cmp(dian a,dian b){
	return a.z<b.z;
} 
int main(){
	freopen("ojilide.in","r",stdin);
	int n=0;
	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-1),cmp);
	double ans=0;
	for(int i=1;i<=n-1;i++){
		ans=ans+sqrt(pow(a[i].x-a[i-1].x,2)+pow(a[i].y-a[i-1].y,2)+pow(a[i].z-a[i-1].z,2));
	}
	cout<<fixed<<setprecision(3)<<ans;
	fclose(stdin);
	return 0;
}