#ifdef _DEBUG
#include "../../library/library/debug_template.cpp"
#define DMP(...) dump(#__VA_ARGS__, __VA_ARGS__)
#else 
#define DMP(...) ((void)0)
#endif

#include <cassert>
#include <cstdio>
#include <cmath>
#include <iostream>
#include <iomanip>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <numeric>
#include <algorithm>

using namespace std;
using lint = long long;
constexpr int MOD = 1000000007, INF = 1010101010;
constexpr lint LINF = 1LL << 60;

struct init {
	init() {
		cin.tie(nullptr); ios::sync_with_stdio(false);
		cout << fixed << setprecision(10);
	}
} init_;

template<class T>
struct Point2D {
	T x, y;
	constexpr Point2D(T x = 0, T y = 0) noexcept : x(x), y(y) {};
	constexpr Point2D(pair<T, T>& p) noexcept : x(p.first), y(p.second) {};
	constexpr bool operator==(const Point2D& rhs) const noexcept { return x == rhs.x && y == rhs.y; }
	constexpr bool operator!=(const Point2D& rhs) const noexcept { return !((*this) == rhs); }
	constexpr bool operator< (const Point2D& rhs) const noexcept { return x < rhs.x || (x == rhs.x && y < rhs.y); }
	constexpr bool operator> (const Point2D& rhs) const noexcept { return rhs < (*this); }
	constexpr bool operator<=(const Point2D& rhs) const noexcept { return !((*this) > rhs); }
	constexpr bool operator>=(const Point2D& rhs) const noexcept { return !((*this) < rhs); }
	constexpr Point2D  operator+ (const Point2D& rhs) const noexcept { return { x + rhs.x, y + rhs.y }; }
	constexpr Point2D  operator- (const Point2D& rhs) const noexcept { return { x - rhs.x, y - rhs.y }; }
	constexpr Point2D  operator* (const T& k) const noexcept { return { k * x, k * y }; }
	constexpr Point2D  operator/ (const T& k) const noexcept { return { x / k, y / k }; }
	constexpr Point2D& operator+=(const Point2D& rhs) noexcept { return ((*this) = (*this) + rhs); }
	constexpr Point2D& operator-=(const Point2D& rhs) noexcept { return ((*this) = (*this) - rhs); }
	constexpr Point2D& operator*=(const T& k) noexcept { return ((*this) = (*this) * k); }
	constexpr Point2D& operator/=(const T& k) noexcept { return ((*this) = (*this) / k); }
	constexpr Point2D  operator- () const noexcept { return { -x, -y }; }
	constexpr T operator* (const Point2D& rhs) const noexcept { return x * rhs.x + y * rhs.y; }
	constexpr Point2D nor() const noexcept { return { y, -x }; }
	constexpr long double hypot() const noexcept { return ::hypotl(x, y); }
	friend istream& operator>>(istream& is, Point2D& p) { return is >> p.x >> p.y; }
	friend ostream& operator<<(ostream& os, const Point2D& p) { return os << p.x << " " << p.y << "\n"; }
	template<class U> U& operator[](vector<vector<U>>& v) { return v[x][y]; }
};

using pnt = Point2D<lint>;

template<class T>
struct Edge {
	int to;
	T cost;
	Edge() {}
	Edge(int to, T cost) : to(to), cost(cost) {}
	bool operator>(const Edge& r) const { return this->cost > r.cost; }
};

template<class T>
vector<T> Dijkstra(const vector<vector<Edge<T>>>& edges, const int st) {

	const int V = (int)edges.size();
	const T inf = numeric_limits<T>::max() / 2;
	vector<T> cost(V, inf);
	cost[st] = 0;

	priority_queue<Edge<T>, vector<Edge<T>>, greater<Edge<T>>> pq;
	pq.emplace(st, cost[st]);

	while (!pq.empty()) {

		Edge<T> now(pq.top().to, pq.top().cost);
		pq.pop();

		if (cost[now.to] < now.cost) continue;
		for (const Edge<T>& e : edges[now.to]) {
			T tmp_cost = now.cost + e.cost;
			if (cost[e.to] > tmp_cost) {
				cost[e.to] = tmp_cost;
				pq.emplace(e.to, cost[e.to]);
			}
		}
	}

	return cost; // min cost to vertex idx from st
}

int main() {

	pnt start, goal;
	cin >> start >> goal;

	int N;
	cin >> N;

	vector<pnt> xy(N);
	vector<int> r(N);
	for (int i = 0; i < N; i++) {
		cin >> xy[i] >> r[i];
	}

	xy.emplace_back(start);
	xy.emplace_back(goal);
	r.emplace_back(0);
	r.emplace_back(0);

	vector<vector<Edge<long double>>> edges(N + 2);
	for (int i = 0; i < N + 2; i++) {
		for (int j = i + 1; j < N + 2; j++) {
			pnt sub = xy[i] - xy[j];
			long double cost = max(sqrtl(sub * sub) - r[i] - r[j], .0L);
			edges[i].emplace_back(j, cost);
			edges[j].emplace_back(i, cost);
			DMP(cost);
		}
	}

	cout << Dijkstra(edges, N).back() << "\n";

	return 0;
}


Measured memory_bytes: 44044