Problem:
Score : 600 points

Problem Statement

On the xy-plane, Snuke is going to travel from the point (x_s, y_s) to the point (x_t, y_t).
He can move in arbitrary directions with speed 1.
Here, we will consider him as a point without size.

There are N circular barriers deployed on the plane.
The center and the radius of the i-th barrier are (x_i, y_i) and r_i, respectively.
The barriers may overlap or contain each other.

A point on the plane is exposed to cosmic rays if the point is not within any of the barriers.

Snuke wants to avoid exposure to cosmic rays as much as possible during the travel.
Find the minimum possible duration of time he is exposed to cosmic rays during the travel.

Constraints

All input values are integers.

-10^9 ≤ x_s, y_s, x_t, y_t ≤ 10^9

(x_s, y_s) ≠ (x_t, y_t)

1≤N≤1,000

-10^9 ≤ x_i, y_i ≤ 10^9

1 ≤ r_i ≤ 10^9

Input

The input is given from Standard Input in the following format:

x_s y_s x_t y_t
N
x_1 y_1 r_1
x_2 y_2 r_2
:
x_N y_N r_N

Output

Print the minimum possible duration of time Snuke is exposed to cosmic rays during the travel.
The output is considered correct if the absolute or relative error is at most 10^{-9}.

Sample Input 1

-2 -2 2 2
1
0 0 1

Sample Output 1

3.6568542495

An optimal route is as follows:

Sample Input 2

-2 0 2 0
2
-1 0 2
1 0 2

Sample Output 2

0.0000000000

An optimal route is as follows:

Sample Input 3

4 -2 -2 4
3
0 0 2
4 0 1
0 4 1

Sample Output 3

4.0000000000

An optimal route is as follows:

Solution in Rust (1.42.0) (judge verdict: Accepted)

#![allow(unused_parens)]
#![allow(unused_imports)]
#![allow(non_upper_case_globals)]
#![allow(non_snake_case)]
#![allow(unused_mut)]
#![allow(unused_variables)]
#![allow(dead_code)]

use itertools::Itertools;
use proconio::input;
use proconio::marker::{Chars, Usize1};

#[allow(unused_macros)]
#[cfg(debug_assertions)]
macro_rules! mydbg {
    //($arg:expr) => (dbg!($arg))
    //($arg:expr) => (println!("{:?}",$arg));
      ($($a:expr),*) => {
          eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
      }
}
#[cfg(not(debug_assertions))]
macro_rules! mydbg {
    ($($arg:expr),*) => {};
}

macro_rules! echo {
    ($($a:expr),*) => {
          $(println!("{}",$a))*
      }
}

use std::cmp::*;
use std::collections::*;
use std::ops::{Add, Div, Mul, Sub};

#[allow(dead_code)]
static INF_I64: i64 = 92233720368547758;
#[allow(dead_code)]
static INF_I32: i32 = 21474836;
#[allow(dead_code)]
static INF_USIZE: usize = 18446744073709551;
#[allow(dead_code)]
static M_O_D: usize = 1000000007;
#[allow(dead_code)]
static PAI: f64 = 3.1415926535897932;

trait IteratorExt: Iterator {
    fn toVec(self) -> Vec<Self::Item>;
}

impl<T: Iterator> IteratorExt for T {
    fn toVec(self) -> Vec<Self::Item> {
        self.collect()
    }
}

trait CharExt {
    fn toNum(&self) -> usize;
    fn toAlphabetIndex(&self) -> usize;
    fn toNumIndex(&self) -> usize;
}
impl CharExt for char {
    fn toNum(&self) -> usize {
        return *self as usize;
    }
    fn toAlphabetIndex(&self) -> usize {
        return self.toNum() - 'a' as usize;
    }
    fn toNumIndex(&self) -> usize {
        return self.toNum() - '0' as usize;
    }
}

trait VectorExt {
    fn joinToString(&self, s: &str) -> String;
}
impl<T: ToString> VectorExt for Vec<T> {
    fn joinToString(&self, s: &str) -> String {
        return self
            .iter()
            .map(|x| x.to_string())
            .collect::<Vec<_>>()
            .join(s);
    }
}

trait StringExt {
    fn get_reverse(&self) -> String;
}
impl StringExt for String {
    fn get_reverse(&self) -> String {
        self.chars().rev().collect::<String>()
    }
}

trait UsizeExt {
    fn pow(&self, n: usize) -> usize;
}
impl UsizeExt for usize {
    fn pow(&self, n: usize) -> usize {
        return ((*self as u64).pow(n as u32)) as usize;
    }
}
use ordered_float::OrderedFloat;

pub struct Dikstra {
    dist: Vec<f64>,
    start: usize,
}
impl Dikstra {
    pub fn new(g: &Vec<Vec<(f64, usize)>>, start: usize) -> Self {
        let mut d = Dikstra {
            dist: vec![INF_I64 as f64; g.len()],
            start: start,
        };
        d.calc(g);
        return d;
    }
    fn calc(&mut self, g: &Vec<Vec<(f64, usize)>>) {
        let mut used = vec![false; g.len()];
        let mut kouho = std::collections::BinaryHeap::new();
        kouho.push((OrderedFloat(0_f64), self.start));
        while !kouho.is_empty() {
            let (_, k) = kouho.pop().unwrap();
            used[self.start] = true;
            self.dist[self.start] = 0_f64;
            for i in 0..g[k].len() {
                let (d, p) = g[k][i];
                if used[p] {
                    continue;
                }
                if self.dist[p] > self.dist[k] + d as f64 {
                    self.dist[p] = self.dist[k] + d as f64;
                    kouho.push((OrderedFloat(self.dist[p] * -1_f64), p));
                }
            }
        }
    }
    pub fn dist_to(&mut self, x: usize) -> f64 {
        return self.dist[x];
    }
}

fn main() {
    input! {
       sx:f64,
       sy:f64,
       gx:f64,
       gy:f64,
       N:usize,
       mut p:[(f64,f64,f64);N],
    }

    p.push((sx, sy, 0.0));
    let start = p.len() - 1;
    p.push((gx, gy, 0.0));
    let goal = p.len() - 1;

    let mut ans: usize = 0;
    let mut map = vec![vec![]; p.len()];
    for i in 0..p.len() {
        let (x, y, r) = p[i];
        for j in i + 1..p.len() {
            let (x2, y2, r2) = p[j];
            let s = x2 - x;
            let t = y2 - y;
            let dist = (s * s + t * t).sqrt();
            let mut cost = dist - r - r2;
            if cost < 0.0 {
                cost = 0.0;
            }
            map[i].push((cost, j));
            map[j].push((cost, i));
        }
    }

    let mut dik = Dikstra::new(&map, start);
    let ans = dik.dist_to(goal);

    echo!(ans);
}