#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int x[50005],y[50005],z[50005];
int main()
{
	int n=0;
	double tot=0;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>x[i]>>y[i]>>z[i];
	}
	for(int i=1;i<=n;i++)
	{
		tot+=sqrt((x[i]-x[i+1])*(x[i]-x[i+1])+(y[i]-y[i+1])*(y[i]-y[i+1])+(z[i]-z[i+1])*(z[i]-z[i+1]));
	}
	cout<<fixed<<setprecision(3)<<tot;
	cout<<endl;
	return 0;
}