#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx")
#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
using namespace std;
using ll = long long;
using vec = vector<ll>;
using vect = vector<double>;
using Graph = vector<vector<ll>>;
#define endl '\n'
#define loop(i, n) for (register int i = 0; i < n; i++)
#define Loop(i, m, n) for (int i = m; i < n; i++)
#define pool(i, n) for (int i = n; i >= 0; i--)
#define Pool(i, m, n) for (int i = n; i >= m; i--)
#define modd 1000000007ll
//#define modd 998244353ll
#define flagcount(bit) __builtin_popcount(bit)
#define flag(x) (1ll << x)
#define flagadd(bit, x) bit |= flag(x)
#define flagpop(bit, x) bit &= ~flag(x)
#define flagon(bit, i) bit &flag(i)
#define flagoff(bit, i) !(bit & (1ll << i))
#define all(v) v.begin(), v.end()
#define low2way(v, x) lower_bound(all(v), x)
#define high2way(v, x) upper_bound(all(v), x)
#define idx_lower(v, x) (distance(v.begin(), low2way(v, x)))  //配列vでx未満の要素数を返す
#define idx_upper(v, x) (distance(v.begin(), high2way(v, x))) //配列vでx以下の要素数を返す
#define idx_lower2(v, x) (v.size() - idx_lower(v, x))         //配列vでx以上の要素数を返す
#define idx_upper2(v, x) (v.size() - idx_upper(v, x))         //配列vでxより大きい要素の数を返す
#define putout(a) cout << a << '\n'
#define Sum(v) accumulate(all(v), 0ll)
ll ctoi(char c)
{
    if (c >= '0' && c <= '9')
    {
        return c - '0';
    }
    return -1;
}
template <typename T>
string make_string(T N)
{
    string ret;
    T now = N;
    while (now > 0)
    {
        T x = now % 10;
        ret += (char)('0' + x);
        now /= 10;
    }
    reverse(all(ret));
    return ret;
}
template <typename T>
T gcd(T a, T b)
{
    if (a % b == 0)
    {
        return (b);
    }
    else
    {
        return (gcd(b, a % b));
    }
}
template <typename T>
T lcm(T x, T y)
{
    T z = gcd(x, y);
    return x * y / z;
}
template <typename T>
bool primejudge(T n)
{
    if (n < 2)
        return false;
    else if (n == 2)
        return true;
    else if (n % 2 == 0)
        return false;
    double sqrtn = sqrt(n);
    for (T i = 3; i < sqrtn + 1; i++)
    {
        if (n % i == 0)
        {
            return false;
        }
        i++;
    }
    return true;
}
template <typename T>
bool chmax(T &a, const T &b)
{
    if (a < b)
    {
        a = b; // aをbで更新
        return true;
    }
    return false;
}
template <typename T>
bool chmin(T &a, const T &b)
{
    if (a > b)
    {
        a = b; // aをbで更新
        return true;
    }
    return false;
}
//場合によって使い分ける
//const ll dx[4]={1,0,-1,0};
//const ll dy[4]={0,1,0,-1};
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
//vector<vector<ll>> field(h, vector<ll>(w));
template <typename T>
struct edge
{
    int to;
    T cost;
    edge(int t, T c) : to(t), cost(c) {}
};
#define P pair<T, int> //P.first:最短距離,P.second:頂点の番号
//頂点V個の負閉路なし重み付きグラフGにおける始点sからの最短距離を求める
template <typename T>
void dijkstra(vector<vector<edge<T>>> G, vector<T> &dist, int s)
{
    int V = G.size();
    //greater<P>によってfirstが小さい順に取り出される
    priority_queue<P, vector<P>, greater<P>> que;
    for (int i = 0; i < V; i++)
        dist[i] = numeric_limits<T>::max();
    dist[s] = (T)0;
    que.push(P((T)0, s));
    //queが空になるまで繰り返す
    while (!que.empty())
    {
        P p = que.top();
        que.pop();
        int v = p.second;
        if (dist[v] < p.first)
            continue; //すでに最短距離ならスルー
        for (int i = 0; i < G[v].size(); i++)
        {
            edge e = G[v][i];
            //更新作業
            if (dist[e.to] > dist[v] + e.cost)
            {
                dist[e.to] = dist[v] + e.cost;
                que.push(P(dist[e.to], e.to));
            }
        }
    }
}
#undef P
int main()
{
    cout << fixed << setprecision(15);
    long double xs, ys, xg, yg;
    ll N;
    cin >> xs >> ys >> xg >> yg >> N;
    vector<long double> X(N), Y(N), R(N);
    loop(i, N) cin >> X[i] >> Y[i] >> R[i];
    vector<vector<edge<long double>>> G(N + 2);
    loop(i, N)
    {
        //スタート地点と各点を結ぶ
        G[i].push_back(edge(N, max((long double)0.0, sqrt((X[i] - xs) * (X[i] - xs) + (Y[i] - ys) * (Y[i] - ys)) - R[i])));
        G[N].push_back(edge(i, max((long double)0.0, sqrt((X[i] - xs) * (X[i] - xs) + (Y[i] - ys) * (Y[i] - ys)) - R[i])));
        //ゴール地点と各点を結ぶ
        G[i].push_back(edge(N + 1, max((long double)0.0, sqrt((X[i] - xg) * (X[i] - xg) + (Y[i] - yg) * (Y[i] - yg)) - R[i])));
        G[N + 1].push_back(edge(i, max((long double)0.0, sqrt((X[i] - xg) * (X[i] - xg) + (Y[i] - yg) * (Y[i] - yg)) - R[i])));
        //スタート地点とゴール地点を結ぶ
        G[N].push_back(edge(N + 1, max((long double)0.0, sqrt((xg - xs) * (xg - xs) + (yg - ys) * (yg - ys)))));
    }
    loop(i, N)
    {
        loop(j, N)
        {
            G[i].push_back(edge(j, max((long double)0.0, sqrt((X[i] - X[j]) * (X[i] - X[j]) + (Y[i] - Y[j]) * (Y[i] - Y[j])) - (R[i] + R[j]))));
            G[j].push_back(edge(i, max((long double)0.0, sqrt((X[i] - X[j]) * (X[i] - X[j]) + (Y[i] - Y[j]) * (Y[i] - Y[j])) - (R[i] + R[j]))));
        }
    }
    vector<long double> dist(N + 2);
    dijkstra(G, dist, N);
    putout(dist[N + 1]);
    return 0;
}


Measured memory_bytes: 139152