#include<bits/stdc++.h>
#define range(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,b) for(int i = 0; i < (b); i++)
#define all(a) (a).begin(), (a).end()
#define show(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
const double INF = 1.797693134e+308;
using namespace std;


typedef complex<double> Point;
typedef Point Vector;
//線分を表す構造体
struct Segment{ Point p1, p2; };
//直線を表す構造体
typedef Segment Line;
//多角形を表す構造体
typedef vector<Point> Polygon;

namespace std{
    bool operator < (const Point &a, const Point &b){
        return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
    }
    bool operator == (const Point &a, const Point &b){
        return a.real() == b.real() && a.imag() == b.imag();
    }
}

class Circle{
    public:
        Point c;
        double r;
        Circle(Point c = Point(), double r = 0.0): c(c), r(r) {}
};

// 許容する誤差
#define EPS (1e-10)

// ベクトルaの絶対値を求める
//double length = abs(a);

// 2点a,b間の距離を求める
//double distance = abs(a-b);

/*
// ベクトルaの単位ベクトルを求める
Point b = a / abs(a);

// ベクトルaの法線ベクトルn1,n2を求める
Point n1 = a * Point(0, 1);
Point n2 = a * Point(0, -1);
*/

int ccw(Point, Point, Point);

// 2つのスカラーが等しいかどうか
bool EQ(double a, double b){
    return (abs(a - b) < EPS);
}

// 2つのベクトルが等しいかどうか
bool EQV(Vector a, Vector b){
    return ( EQ(a.real(), b.real()) && EQ(a.imag(), b.imag()) );
}

// 内積 (dot product) : a・b = |a||b|cosΘ
double dot(Point a, Point b) {
    return (a.real() * b.real() + a.imag() * b.imag());
}

// 外積 (cross product) : a×b = |a||b|sinΘ
double cross(Point a, Point b) {
    return (a.real() * b.imag() - a.imag() * b.real());
}

// 2直線の直交判定 : a⊥b <=> dot(a, b) = 0
bool isOrthogonal(Point a1, Point a2, Point b1, Point b2) {
    return EQ( dot(a1-a2, b1-b2), 0.0 );
}
bool isOrthogonal(Line s1, Line s2) {
    return isOrthogonal(s1.p1, s1.p2, s2.p1, s2.p2);
}

// 2直線の平行判定 : a//b <=> cross(a, b) = 0
bool isParallel(Point a1, Point a2, Point b1, Point b2) {
    return EQ( cross(a1-a2, b1-b2), 0.0 );
}
bool isParallel(Line s1, Line s2) {
    return isParallel(s1.p1, s1.p2, s2.p1, s2.p2);
}

// 点cが直線a,b上にあるかないか
bool isPointOnLine(Point a, Point b, Point c) {
    return EQ( cross(b-a, c-a), 0.0 );
}
bool isPointOnLine(Line s, Point c) {
    return isPointOnLine(s.p1, s.p2, c);
}

// 点a,bを通る直線と点cとの距離
double distanceLPoint(Point a, Point b, Point c) {
    return abs(cross(b-a, c-a)) / abs(b-a);
}
double distanceLPoint(Line s, Point c) {
    return distanceLPoint(s.p1, s.p2, c);
}

// 点a,bを端点とする線分と点cとの距離
double distanceLsPoint(Point a, Point b, Point c) {
    if ( dot(b-a, c-a) < EPS ) return abs(c-a);
    if ( dot(a-b, c-b) < EPS ) return abs(c-b);
    return abs(cross(b-a, c-a)) / abs(b-a);
}
double distanceLsPoint(Segment s, Point c) {
    return distanceLsPoint(s.p1, s.p2, c);
}

// a1,a2を端点とする線分とb1,b2を端点とする線分の交差判定
bool isIntersectedLs(Point a1, Point a2, Point b1, Point b2) {
    return ( ccw(a1, a2, b1) * ccw(a1, a2, b2) <= 0 &&
            ccw(b1, b2, a1) * ccw(b1, b2, a2) <= 0 );
}
bool isIntersectedLs(Segment s1, Segment s2) {
    return isIntersectedLs(s1.p1, s1.p2, s2.p1, s2.p2);
}

// a1,a2を端点とする線分とb1,b2を端点とする線分の交点計算
Point intersectionLs(Point a1, Point a2, Point b1, Point b2) {
    Vector base = b2 - b1;
    double d1 = abs(cross(base, a1 - b1));
    double d2 = abs(cross(base, a2 - b1));
    double t = d1 / (d1 + d2);

    return Point(a1 + (a2 - a1) * t);
}
Point intersectionLs(Segment s1, Segment s2) {
    return intersectionLs(s1.p1, s1.p2, s2.p1, s2.p2);
}

// a1,a2を通る直線とb1,b2を通る直線の交差判定
bool isIntersectedL(Point a1, Point a2, Point b1, Point b2) {
    return !EQ( cross(a1-a2, b1-b2), 0.0 );
}
bool isIntersectedL(Line l1, Line l2) {
    return isIntersectedL(l1.p1, l1.p2, l2.p1, l2.p2);
}

// a1,a2を通る直線とb1,b2を通る直線の交点計算
Point intersectionL(Point a1, Point a2, Point b1, Point b2) {
    Point a = a2 - a1; Point b = b2 - b1;
    return a1 + a * cross(b, b1-a1) / cross(b, a);
}
Point intersectionL(Line l1, Line l2) {
    return intersectionL(l1.p1, l1.p2, l2.p1, l2.p2);
}

// 線分s1と線分s2の距離
double distanceLL(Segment s1, Segment s2){
    if(isIntersectedLs(s1.p1, s1.p2, s2.p1, s2.p2) ) return 0.0;
    return min(
            min(distanceLsPoint(s1.p1, s1.p2, s2.p1),
                distanceLsPoint(s1.p1, s1.p2, s2.p2)),
            min(distanceLsPoint(s2.p1, s2.p2, s1.p1),
                distanceLsPoint(s2.p1, s2.p2, s1.p2)) );
}

// 線分sに対する点pの射影
Point project(Segment s, Point p){
    Vector base = s.p2 - s.p1;
    double r = dot(p - s.p1, base) / norm(base);
    return Point(s.p1 + base * r);
}

//線分sを対象軸とした点pの線対称の点
Point reflect(Segment s, Point p){
    return Point(p + (project(s, p) - p) * 2.0);
}

//点pをangle分だけ時計回りに回転
Point rotation(Point p, double angle){
    double x, y;
    x = p.real() * cos(angle) - p.imag() * sin(angle);
    y = p.real() * sin(angle) + p.imag() * cos(angle);
    return Point(x, y);
}

//円cと線分lの交点
pair<Point, Point> getCrossPoints(Circle c, Line l){
    Vector pr = project(l, c.c);
    Vector e = (l.p2 - l.p1) / abs(l.p2 - l.p1);
    double base = sqrt(c.r * c.r - norm(pr - c.c));
    return make_pair(pr + e * base, pr - e * base);
}

//円c1と円c2の交点
double arg(Vector p) { return atan2(p.imag(), p.real()); }
Vector polar(double a, double r) { return Point(cos(r) * a, sin(r) *a); }

pair<Point, Point> getCrossPoints(Circle c1, Circle c2){
    double d = abs(c1.c - c2.c);
    double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
    double t = arg(c2.c - c1.c);
    return make_pair(Point(c1.c + polar(c1.r, t + a)), Point(c1.c + polar(c1.r, t - a)));
}

//点の内包
static const int IN = 2;
static const int ON = 1;
static const int OUT = 0;

int contains(Polygon g, Point p){
    int n = g.size();
    bool x = false;
    rep(i,n){
        Point a = g[i] - p, b = g[(i + 1) % n] - p;
        if( abs(cross(a, b)) < EPS && dot(a,  b) < EPS ) return ON;
        if( a.imag() > b.imag() ) swap(a, b);
        if( a.imag() < EPS && EPS < b.imag() && cross(a, b) > EPS ) x = not x;
    }
    return ( x ? IN : OUT );
}

//ベクトルの位置検出
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;

int ccw(Point p0, Point p1, Point p2){
    Vector a = p1 - p0;
    Vector b = p2 - p0;
    if( cross(a, b) > EPS ) return COUNTER_CLOCKWISE;
    if( cross(a, b) < -EPS ) return CLOCKWISE;
    if( dot(a, b) < -EPS ) return ONLINE_BACK;
    if( abs(a) < abs(b) ) return ONLINE_FRONT;

    return ON_SEGMENT;
}

//凸包
Polygon andrewScan( Polygon s ){
    Polygon u, l;
    if( s.size() < 3 ) return s;
    sort(s.begin(), s.end());

    u.emplace_back(s[0]);
    u.emplace_back(s[1]);

    l.emplace_back(s[s.size() - 1]);
    l.emplace_back(s[s.size() - 2]);

    range(i,2,s.size()){
        //== COUNTER_CLOCKWISEだと内角は180以下（一直線上に並んでいても、頂点として数える）
        //!= CLOCKWISEだと内角は180未満（一直線上の頂点は数えない）
        for(int n = u.size(); n >= 2 && ccw(u[n-2], u[n-1], s[i]) != CLOCKWISE; n--){
            u.pop_back();
        }
        u.emplace_back(s[i]);
    }

    for(int i = s.size() - 3; i >= 0; i--){
        for(int n = l.size(); n >= 2 && ccw(l[n-2], l[n-1], s[i]) != CLOCKWISE; n--){
            l.pop_back();
        }
        l.emplace_back(s[i]);
    }

    reverse(l.begin(), l.end());
    for(int i = u.size() - 2; i >= 1; i--) l.emplace_back(u[i]);

    return l;
}

class Node{
    public:
        double dis;
        bool isUsed;
        Node(){
            this->dis = INF;
            this->isUsed = 0;
        }
};

vector<Circle> cir;

double dijkstra(int n, double a[1005][1005]){
    assert(n < 1005);
    vector<Node> node(n);
    priority_queue<int, vector<pair<double, int>>, greater<pair<double, int>>> q;

    q.push(make_pair(0.0, 0));
    node[0].dis = 0.0;

    pair<double, int> u;
    while(not q.empty()){
        u = q.top(); q.pop();
        int current = u.second;
        node[current].isUsed = 1;

        rep(i,n){
            if(node[i].isUsed == 0){
                if(node[i].dis > node[current].dis + a[current][i]){
                    node[i].dis = node[current].dis + a[current][i];
                    q.push(make_pair(node[i].dis, i));
                }
            }
        }
    }
    return node[1].dis;
}

int main(){
    int n;

    double sx, sy, tx, ty;
    cin >> sx >> sy >> tx >> ty;
    Point s = Point{sx, sy};
    Point t = Point{tx, ty};
    cir.emplace_back(s, 0);
    cir.emplace_back(t, 0);

    cin >> n;
    rep(i,n){
        double a, b, c;
        cin >> a >> b >> c;
        cir.emplace_back(Circle{Point{a, b}, c});
    }

    double a[1005][1005];
    rep(i,cir.size()){
        rep(j,cir.size()){
            a[i][j] = max(0.0, abs(cir[i].c - cir[j].c) - (cir[i].r + cir[j].r));
            //show(a[i][j])
        }
    }
    cout <<fixed << setprecision(12) << dijkstra(cir.size(), a) << endl;
}


Measured memory_bytes: 12412