#include <cstdio>
#include <cstdint>
#include <vector>
#include <algorithm>
#include <utility>
#include <limits>
#include <queue>
#include <complex>
#include <tuple>

template <typename WeightType>
class weighted_edge {
public:
  using size_type = size_t;
  using weight_type = WeightType;

protected:
  size_type M_src, M_dst;
  weight_type M_weight;

public:
  weighted_edge() = default;
  weighted_edge(weighted_edge const&) = default;
  weighted_edge(weighted_edge&&) = default;

  weighted_edge(size_type s, size_type d, weight_type w):
    M_src(s), M_dst(d), M_weight(w)
  {}

  weighted_edge& operator =(weighted_edge const&) = default;
  weighted_edge& operator =(weighted_edge&&) = default;

  bool operator <(weighted_edge const& other) const {
    if (M_weight < other.M_weight) return true;
    if (other.M_weight < M_weight) return false;
    if (M_src != other.M_src) return M_src < other.M_src;
    return M_dst < other.M_dst;
  }

  size_type source() const { return M_src; }
  size_type target() const { return M_dst; }
  weight_type weight() const { return M_weight; }
};

struct directed_tag {};
struct undirected_tag {};

template <typename Edge, typename Directedness>
class adjacency_list {
public:
  using size_type = size_t;
  using edge_type = Edge;
  using weight_type = typename Edge::weight_type;
  static constexpr weight_type inf = std::numeric_limits<weight_type>::max();

private:
  std::vector<std::vector<edge_type>> M_g;

public:
  adjacency_list() = default;
  adjacency_list(adjacency_list const&) = default;
  adjacency_list(adjacency_list&&) = default;
  adjacency_list(size_type n): M_g(n) {}

  template <typename... Args>
  void emplace(size_type src, size_type dst, Args... args) {
    M_g[src].emplace_back(src, dst, args...);
    if (std::is_same<Directedness, undirected_tag>::value)
      M_g[dst].emplace_back(dst, src, args...);
  }

  size_type size() const { return M_g.size(); }
  std::vector<edge_type> const& operator [](size_type i) const { return M_g[i]; }
};

template <typename Edge, typename Directedness>
constexpr typename Edge::weight_type adjacency_list<Edge, Directedness>::inf;

struct dijkstra_tag {} dijkstra;

template <typename Edge, typename Directedness>
auto shortest(adjacency_list<Edge, Directedness> const& g, size_t s, dijkstra_tag) {
  using weight_type = typename Edge::weight_type;
  using pair_type = std::pair<weight_type, size_t>;
  size_t n = g.size();
  std::vector<weight_type> dp(n, std::numeric_limits<weight_type>::max());
  dp[s] = weight_type(0);
  std::priority_queue<pair_type, std::vector<pair_type>, std::greater<>> pq;
  pq.emplace(weight_type(0), s);
  while (!pq.empty()) {
    weight_type w;
    size_t v;
    std::tie(w, v) = pq.top();
    pq.pop();
    if (dp[v] < w) continue;
    for (auto const& e: g[v]) {
      weight_type nw = dp[e.source()] + e.weight();
      size_t nv = e.target();
      if (nw < dp[nv]) {
        dp[nv] = nw;
        pq.emplace(std::move(nw), nv);
      }
    }
  }
  return dp;
}

int main() {
  double xs, ys, xt, yt;
  scanf("%lf %lf %lf %lf", &xs, &ys, &xt, &yt);

  size_t n;
  scanf("%zu", &n);

  std::vector<std::pair<std::complex<double>, double>> c(n);
  for (auto& ci: c) {
    double x, y, r;
    scanf("%lf %lf %lf", &x, &y, &r);

    std::complex<double> z(x, y);
    ci = std::make_pair(z, r);
  }
  c.emplace_back(std::complex<double>(xs, ys), 0.0);
  c.emplace_back(std::complex<double>(xt, yt), 0.0);
  n += 2;

  adjacency_list<weighted_edge<double>, undirected_tag> g(n);
  for (size_t i = 0; i < n; ++i) {
    std::complex<double> zi;
    double ri;
    std::tie(zi, ri) = c[i];
    for (size_t j = 0; j < i; ++j) {
      std::complex<double> zj;
      double rj;
      std::tie(zj, rj) = c[j];

      double w = std::max(0.0, std::abs(zi-zj) - (ri+rj));
      g.emplace(i, j, w);
    }
  }

  printf("%.12f\n", shortest(g, n-2, dijkstra)[n-1]);
}


Measured memory_bytes: 29936