#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <vector>

const int MOD = 1e9 + 7;
const int iINF = 2147483647 / 2;
const long long int llINF = 9223372036854775807 / 2;

using namespace std;
using ll = long long int;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vvvl = vector<vector<vector<ll>>>;

typedef pair<ll, ll> pll;
bool paircomp(const pll &a, const pll &b) {
  if (a.first == b.first)
    return a.second < b.second;
  return a.first < b.first;
}

#define REP(i, n) for (ll i = 0; i < (n); i++)
#define RREP(i, n) for (ll i = (n)-1; i >= 0; i--)
#define FOR(i, a, b) for (ll i = (a); i < (b); i++)
#define AUTO(i, m) for (auto &i : m)
#define ALL(a) (a).begin(), (a).end()
#define MAX(vec) *std::max_element(vec.begin(), vec.end())
#define MIN(vec) *std::min_element(vec.begin(), vec.end())
#define ARGMAX(vec)                                                            \
  std::distance(vec.begin(), std::max_element(vec.begin(), vec.end()))
#define ARGMIN(vec)                                                            \
  std::distance(vec.begin(), std::min_element(vec.begin(), vec.end()))
#define REV(T) greater<T>()
#define PQ(T) priority_queue<T, vector<T>, greater<T>>
#define VVL(a, b, c) vector<vector<ll>>(a, vector<ll>(b, c))
#define VV(T, a, b, c) vector<vector<T>>(a, vector<T>(b, c))
#define VVVL(a, b, c, d)                                                       \
  vector<vector<vector<ll>>>(a, vector<vector<ll>>(b, vector<ll>(c, d)))
#define VVV(T, a, b, c, d)                                                     \
  vector<vector<vector<T>>>(a, vector<vector<T>>(b, vector<T>(c, d)))
#define SP(a) setprecision(a)
#define SQRT(a) sqrt((long double)(a))
#define DPOW(a, b) pow((long double)(a), (long double)(b))
#define UNIQUE(vec)                                                            \
  do {                                                                         \
    sort(ALL((vec)));                                                          \
    (vec).erase(std::unique(ALL((vec))), (vec).end());                         \
  } while (0)

ll POW(ll n, ll m) {
  if (m == 0) {
    return 1;
  } else if (m % 2 == 0) {
    ll tmp = POW(n, m / 2);
    return (tmp * tmp);
  } else {
    return (n * POW(n, m - 1));
  }
}

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

typedef long double Weight;
struct Edge {
  ll src, dst;
  Weight weight;
  Edge(ll src, ll dst, Weight weight) : src(src), dst(dst), weight(weight) {}
};
bool operator<(const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
             e.src != f.src ? e.src < f.src : e.dst < f.dst;
}

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

typedef vector<Weight> Array;
typedef vector<Array> Matrix;

void shortestPath(const Graph &g, ll s, vector<Weight> &dist,
                  vector<ll> &prev) {
  ll n = g.size();
  dist.assign(n, llINF);
  dist[s] = 0;
  prev.assign(n, -1);
  priority_queue<Edge> Q; // "e < f" <=> "e.weight > f.weight"
  for (Q.push(Edge(-2, s, 0)); !Q.empty();) {
    Edge e = Q.top();
    Q.pop();
    if (prev[e.dst] != -1)
      continue;
    prev[e.dst] = e.src;
    AUTO(f, g[e.dst]) {
      if (dist[f.dst] > e.weight + f.weight) {
        dist[f.dst] = e.weight + f.weight;
        Q.push(Edge(f.src, f.dst, e.weight + f.weight));
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll xs, ys, xt, yt, N;
  cin >> xs >> ys >> xt >> yt >> N;
  Graph G(N + 2);
  vl X(N + 2, 0);
  vl Y(N + 2, 0);
  vector<long double> R(N + 2, 0);
  X[0] = xs;
  X[N + 1] = xt;
  Y[0] = ys;
  Y[N + 1] = yt;
  FOR(i, 1, N + 1) { cin >> X[i] >> Y[i] >> R[i]; }
  REP(i, N + 2) REP(j, N + 2) {
    long double kyori = SQRT(DPOW(X[i] - X[j], 2) + DPOW(Y[i] - Y[j], 2));
    long double d = max(kyori - (R[i] + R[j]), (long double)0.0);
    G[i].push_back(Edge(i, j, d));
    G[j].push_back(Edge(j, i, d));
  }
  vector<Weight> dist(N + 2);
  vl prev(N + 2);
  shortestPath(G, 0, dist, prev);
  cout << fixed << SP(20) << dist[N + 1] << endl;
  return 0;
}


Measured memory_bytes: 75504