use std::ops::DivAssign;
use std::ops::MulAssign;
use std::ops::SubAssign;
use std::collections::BinaryHeap;
use std::str::FromStr;
use std::collections::HashSet;
use std::collections::BTreeMap;
use std::fmt::Display;
use std::ops::Neg;
use std::ops::Div;
use std::ops::Mul;
use std::ops::Add;
use std::ops::{AddAssign, Sub};
use std::cmp::max;
use std::collections::VecDeque;
use std::cmp::min;
use std::collections::{HashMap, BTreeSet};
use std::cmp::Ordering;
use std::fmt::Debug;

fn read_line() -> String {
    let mut buffer = String::new();
    std::io::stdin().read_line(&mut buffer).expect("No Line");
    buffer.trim().to_owned()
}
fn read_lines<T: std::str::FromStr>(count: usize) -> Vec<T> {
    let mut buffer = String::new();
    let mut vec = Vec::with_capacity(count);
    for _ in 0 .. count {
        std::io::stdin().read_line(&mut buffer).expect("No Line");
        vec.push(buffer.trim().parse().ok().expect("Can't Parse"));
        buffer.clear();
    }
    vec
}
fn read_tabulate<R, T: Fn(&str)->R> (count: usize, transformer: T) -> Vec<R> {
    let mut buffer = String::new();
    let mut vec = Vec::with_capacity(count);
    for _ in 0 .. count {
        std::io::stdin().read_line(&mut buffer).expect("No Line");
        vec.push(transformer(buffer.trim()));
        buffer.clear();
    }
    vec
}
fn read_value<T: std::str::FromStr>() -> T {
    read_line().trim().parse().ok().unwrap()
}
fn read_values<T: std::str::FromStr>() -> Vec<T> {
    read_line().trim().split(' ').map(|x| x.parse().ok().expect("Can't Parse")).collect::<Vec<T>>()
}
macro_rules! freeze {
    ($($id:ident), *) => {
        $(let $id = $id;)*
    };
}
macro_rules! read_map {
    ($ident: ident: [$block: block; $size: expr]) => {
        let $ident = (0 .. $size).into_iter().map(|_| $block).collect::<Vec<_>>();
    };
    (mut $ident: ident: [$block: block; $size: expr]) => {
        let mut $ident = (0 .. $size).into_iter().map(|_| $block).collect::<Vec<_>>();
    };
}
macro_rules! read {
    (mut $ident: ident: [$ty:ty]) => {
        let mut $ident = read_values::<$ty>();
    };
    ($ident: ident: [$ty:ty]) => {
        let $ident = read_values::<$ty>();
    };
    (mut $ident: ident: [[$ty:ty]; $size: expr]) => {
        let mut $ident = (0 .. $size).into_iter().map(|_| read_values::<$ty>()).collect::<Vec<_>>();
    };
    ($ident: ident: [[$ty:ty]; $size: expr]) => {
        let $ident = (0 .. $size).into_iter().map(|_| read_values::<$ty>()).collect::<Vec<_>>();
    };
    (mut $ident: ident: [$ty:ty; $size:expr]) => {
        let mut $ident = read_lines::<$ty>($size);
    };
    ($ident: ident: [$ty:ty; $size:expr]) => {
        let $ident = read_lines::<$ty>($size);
    };
    ($ident: ident: [$block: block; $size: expr]) => {
        let $ident = (0 .. $size).into_iter().map(|_| $block).collect::<Vec<_>>();
    };
    (mut $ident: ident: [$block: block; $size: expr]) => {
        let mut $ident = (0 .. $size).into_iter().map(|_| $block).collect::<Vec<_>>();
    };
    ($($token: tt)*) => {
        let mut iter = read_values::<String>().into_iter();
        read_from_iter!(iter; $($token)*);
    };
}
macro_rules! read_from_iter {
    ($iter:expr; mut $ident:ident:$ty:ty, $($rest:tt)*) => {
        let mut $ident = $iter.next().unwrap().parse::<$ty>().expect("Can't Parse");
        read_from_iter!($iter; $($rest)*);
    };
    ($iter:expr; $ident:ident:$ty:ty, $($rest:tt)*) => {
        let $ident = $iter.next().unwrap().parse::<$ty>().expect("Can't Parse");
        read_from_iter!($iter; $($rest)*);
    };
    ($iter:expr; mut $ident:ident:$ty:ty) => {
        let mut $ident = $iter.next().unwrap().parse::<$ty>().expect("Can't Parse");
    };
    ($iter:expr; $ident:ident:$ty:ty) => {
        let $ident = $iter.next().unwrap().parse::<$ty>().expect("Can't Parse");
    };
    ($iter: expr; ) => {};
}
struct KeyValue<K, V> {
    key: K,
    value: V
}
impl <K: PartialOrd, V> PartialEq for KeyValue<K, V> {
    fn eq(&self, other: &Self) -> bool {
        self.key.eq(&other.key)
    }
}
impl <K: PartialOrd, V> Eq for KeyValue<K, V> {}
impl <K: PartialOrd, V> PartialOrd for KeyValue<K, V> {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        self.key.partial_cmp(&other.key)
    }
}
impl <K: PartialOrd, V> Ord for KeyValue<K, V> {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.key.partial_cmp(&other.key).ok_or("Can't Compare").unwrap()
    }
}
#[derive(Copy, Clone, Debug)]
struct Point {
    x: f64, y: f64, z: f64
}
impl Point {
    fn distance(&self, other: &Point) -> f64 {
        let dx = self.x - other.x;
        let dy = self.y - other.y;
        let dz = self.z - other.z;
        (dx * dx + dy * dy + dz * dz).sqrt()
    }
}
#[derive(Copy, Clone, Debug)]
struct Circle {
    center: Point, radius: f64
}
impl Circle {
    fn corridor_length(&self, other: &Circle) -> f64 {
        let len = self.center.distance(&other.center) - self.radius - other.radius;
        if len > 0f64 {
            len
        }else {
            0f64
        }
    }
}
#[derive(Clone, Debug)]
struct UnionFind {
    vec: Vec<i32>
}
impl UnionFind {
    fn new(size: usize) -> UnionFind {
        UnionFind{vec: vec![-1; size]}
    }
    fn find(&mut self, a: usize) -> usize {
        if self.vec[a] < 0 {
            a
        }else {
            let parent = self.vec[a] as usize;
            let root = self.find(parent);
            self.vec[a] = root as i32;
            root
        }
    }
    fn same(&mut self, a: usize, b: usize) -> bool {
        self.find(a) == self.find(b)
    }
    fn unite(&mut self, mut a: usize, mut b: usize) {
        a = self.find(a);
        b = self.find(b);
        if a != b {
            if self.vec[a] < self.vec[b] {
                self.vec[a] += self.vec[b];
                self.vec[b] = a as i32;
            }else {
                self.vec[b] += self.vec[a];
                self.vec[a] = b as i32;
            }
        }
    }
}

fn main() {
    loop {
        read!(n: usize);
        if n == 0 {break;}
        read_map!(balls: [{
            read!(x: f64, y: f64, z: f64, r: f64);
            Circle{center: Point{x: x, y: y, z: z}, radius: r}
        }; n]);
        let mut uft = UnionFind::new(n);
        let mut edges = Vec::new();
        for i in 0 .. n {
            for j in 0 .. i {
                let len = balls[i].corridor_length(&balls[j]);
                if len == 0f64 {
                    uft.unite(i, j);
                }else {
                    edges.push((i, j, len));
                }
            }
        }
        edges.sort_by(|a, b| a.2.partial_cmp(&b.2).unwrap());
        let mut result = 0f64;
        for (i, j, len) in edges {
            if !uft.same(i, j) {
                result += len;
                uft.unite(i, j);
            }
        }
        println!("{:.*}", 3, result);
    }
}


Measured memory_bytes: 5108