#include<bits/stdc++.h>
using namespace std;
struct point {
int x, y, z;
};
double o(int x, int y, int z, int a, int b ,int c) {
return sqrt(pow(x - a, 2) + pow(y - b, 2) + pow(z - c, 2));
}
bool cmp(point a, point b) {
return a.z < b.z;
}
int main()
{
int n;
cin >> n;
point p[50001];
for (int i = 0; i < n; i++) {
cin >> p[i].x >> p[i].y >> p[i].z;
}
sort(p, p + n, cmp);
double sum=0;
for (int i = 0; i < n; i++) {
sum += o(p[i].x, p[i].y, p[i].z, p[i + 1].x, p[i + 1].y, p[i + 1].z);
}
printf("%3d",sum);
}