// template version 1.15
using namespace std;
#include <bits/stdc++.h>

// varibable settings
#define int long long
const int INF=1e18;

// define basic macro {{{
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)((b)-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define each(i,a) for (auto&& i : a)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define mt(a, b, c) make_tuple(a, b, c)
#define divceil(a,b) ((a)+(b)-1)/(b)
#define is_in(x, a, b) ((a)<=(x) && (x)<(b))
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
#define ub upper_bound
#define lb lower_bound
#define posl(A, x) (lower_bound(all(A), x)-A.begin())
#define posu(A, x) (upper_bound(all(A),x)-A.begin())
template<class T> inline void chmax(T &a, const T &b) { if((a) < (b)) (a) = (b); }
template<class T> inline void chmin(T &a, const T &b) { if((a) > (b)) (a) = (b); }

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;

template<typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;

void sputs(){}
template <class Head, class... Tail>
void sputs(Head&& head, Tail&&... tail) {
  cout << head;
  if (sizeof...(Tail) == 0) { cout << endl; }
  else { cout << " "; }
  sputs(std::move(tail)...);
}

#if defined(PCM) || defined(LOCAL)
  #include "lib/dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif
//}}}


using COST = double;
using POS = int;
using EDGE = pair<POS, COST>;
struct GRAPH{
  map<POS, vector<EDGE>> all_edges;
  vector<POS> all_nodes;

  void add_edge(POS from, POS to, COST cost){
    all_edges[from].emplace_back(mp(to, cost));
  }

  auto operator[](POS pos){
    return all_edges[pos];
  }
};
auto& operator<<(auto& stream, GRAPH G){
  stream << G.all_edges;
  return stream;
}

map<POS, COST> dijkstra(GRAPH& G, POS start){
  map<POS, COST> d;  // 最短距離
  each(node, G.all_nodes) {d[node] = INF;}

  PQ<pair<COST, POS>> q;
  q.push(mp(0LL, start));
  while (!q.empty()){
    auto cp = q.top(); q.pop();
    auto cost = cp.first;
    auto pos = cp.second;

    if (cost < d[pos]) {
      d[pos] = cost;
      for (const auto &el:G[pos]){
        auto ncost = cost + el.second;
        auto npos = el.first;
        if (ncost < d[npos]) q.push(mp(ncost, npos));
      }
    }
  }
  return d;
}

// int sample(){
//   return 0;
// }


signed main() {
  int sx,sy,gx,gy;cin>>sx>>sy>>gx>>gy;
  int n;cin>>n;
  vi x(n+2),y(n+2),r(n+2);
  rep(i,n)cin>>x[i+1]>>y[i+1]>>r[i+1];
  dump(r);
  x[0] = sx; y[0] = sy; r[0] = 0;
  x[n+1] = gx; y[n+1] = gy; r[n+1] = 0;

  GRAPH G;
  rep(i, n+2) G.all_nodes.pb(i);  // add node
  rep(i, n+2){
    rep(j, i+1, n+2){
      double d = sqrt((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));
      double cost = max(0.0, d - r[i] - r[j]);
      G.add_edge(i, j, cost);
      G.add_edge(j, i, cost);
    }
  }
  dump(G);

  // calc min distance by G
  auto d = dijkstra(G, 0);
  printf("%.15f", d[n+1]);

  return 0;
}


Measured memory_bytes: 26732