#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);
}