#include<stdio.h>
#include<math.h>
struct den{
	int x,y,z;
}den[50005];

int main()
{
	int n;
	scanf("%d", &n );
	for ( int i = 1; i <= n; i++ ) {
		scanf("%d %d %d", &den[i].x, &den[i].y, &den[i].z );
	}
	
	struct den t;
	for ( int i = 2; i <= n; i++ ) {
		for ( int j = i+1; j <= n; j++ )
		if ( den[i].z > den[j].z ) {
			t = den[i];
			den[i] = den[j];
			den[j] = t;
		}
	}
	
	double sum = 0;
	for ( int i = 2; i <= n; i++ ) {
		sum += sqrt( pow(den[i-1].x-den[i].x,2)+pow(den[i-1].y-den[i].y,2)+pow(den[i-1].z-den[i].z,2) );
	}
	printf("%.3lf", sum );
	return 0;
}