#include <stdio.h>
#include <math.h>
int main()
{
	int n,a[50010],b[50010],c[50010],i,j;
	double d = 0.0;
	int term1,term2,term3;
	scanf("%d",&n);
	for(i=1;i<=n;i++){
		scanf("%d%d%d",&a[i],&b[i],&c[i]);
	}
	for(i=1;i<n;i++){
		for(j=i+1;j<=n;j++){
			if(c[j]<c[i]){
				term1 = a[j];
				a[j] = a[i];
				a[i] = term1;
				term2 = b[j];
				b[j] = b[i];
				b[i] = term2;
				term3 = c[j];
				c[j] = c[i];
				c[i] = term3;
			}
		}
	}
	for(i=1;i<n;i++){
		d += sqrt((a[i+1]-a[i])*(a[i+1]-a[i])+(b[i+1]-b[i])*(b[i+1]-b[i])+(c[i+1]-c[i])*(c[i+1]-c[i]));
	}
	printf("%.3lf",d);
	return 0;
}