#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>
#include <random>
#include <chrono>
#include <cassert>
#include <tuple>
#include <utility>
using namespace std;

namespace {
  using Integer = long long; //__int128;
  template<class T, class S> istream& operator >> (istream& is, pair<T,S>& p){return is >> p.first >> p.second;}
  template<class T> istream& operator >> (istream& is, vector<T>& vec){for(T& val: vec) is >> val; return is;}
  template<class T> istream& operator ,  (istream& is, T& val){ return is >> val;}
  template<class T, class S> ostream& operator << (ostream& os, const pair<T,S>& p){return os << p.first << " " << p.second;}
  template<class T> ostream& operator << (ostream& os, const vector<T>& vec){for(size_t i=0; i<vec.size(); i++) os << vec[i] << (i==vec.size()-1?"":" "); return os;}
  template<class T> ostream& operator ,  (ostream& os, const T& val){ return os << " " << val;}

  template<class H> void print(const H& head){ cout << head; }
  template<class H, class ... T> void print(const H& head, const T& ... tail){ cout << head << " "; print(tail...); }
  template<class ... T> void println(const T& ... values){ print(values...); cout << endl; }

  template<class H> void eprint(const H& head){ cerr << head; }
  template<class H, class ... T> void eprint(const H& head, const T& ... tail){ cerr << head << " "; eprint(tail...); }
  template<class ... T> void eprintln(const T& ... values){ eprint(values...); cerr << endl; }

  class range{ Integer start_, end_, step_; public: struct range_iterator{ Integer val, step_; range_iterator(Integer v, Integer step) : val(v), step_(step) {} Integer operator * (){return val;} void operator ++ (){val += step_;} bool operator != (range_iterator& x){return step_ > 0 ? val < x.val : val > x.val;} }; range(Integer len) : start_(0), end_(len), step_(1) {} range(Integer start, Integer end) : start_(start), end_(end), step_(1) {} range(Integer start, Integer end, Integer step) : start_(start), end_(end), step_(step) {} range_iterator begin(){ return range_iterator(start_, step_); } range_iterator   end(){ return range_iterator(  end_, step_); } };

  inline string operator "" _s (const char* str, size_t size){ return move(string(str)); }
  constexpr Integer my_pow(Integer x, Integer k, Integer z=1){return k==0 ? z : k==1 ? z*x : (k&1) ? my_pow(x*x,k>>1,z*x) : my_pow(x*x,k>>1,z);}
  constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z=1){return k==0 ? z%M : k==1 ? z*x%M : (k&1) ? my_pow_mod(x*x%M,k>>1,M,z*x%M) : my_pow_mod(x*x%M,k>>1,M,z);}
  constexpr unsigned long long operator "" _ten (unsigned long long value){ return my_pow(10,value); }

  inline int k_bit(Integer x, int k){return (x>>k)&1;} //0-indexed

  mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count());

  template<class T> string join(const vector<T>& v, const string& sep){ stringstream ss; for(size_t i=0; i<v.size(); i++){ if(i>0) ss << sep; ss << v[i]; } return ss.str(); }

  inline string operator * (string s, int k){ string ret; while(k){ if(k&1) ret += s; s += s; k >>= 1; } return ret; }
}
constexpr long long mod = 9_ten + 7;

using real = long double;

int main(){
  long long x0,y0,x1,y1;
  cin >>  x0,y0,x1,y1;
  int n;
  cin >> n;
  vector<long long> x(n),y(n),r(n);
  for(auto i : range(n) ){
    cin >> x[i],y[i],r[i];
  }

  vector<vector<real>> dist(n+2, vector<real>(n+2, 1e18));
  for(auto i : range(n) ){
    real d = sqrt( pow(x[i]-x0,2) + pow(y[i]-y0,2) );
    d = max<real>(0.0, d-r[i]);
    dist[i][n] = dist[n][i] = min(dist[n][i], d);
  }
  for(auto i : range(n) ){
    real d = sqrt( pow(x[i]-x1,2) + pow(y[i]-y1,2) );
    d = max<real>(0.0, d-r[i]);
    dist[i][n+1] = dist[n+1][i] = min(dist[n+1][i], d);
  }

  {
    real d = sqrt( pow(x0-x1, 2) + pow(y0-y1, 2) );
    dist[n][n+1] = dist[n+1][n] = d;
  }

  for(auto i : range(n) ){
    dist[i][i] = 0.0;
    for(auto j : range(i+1, n) ){
      real d = sqrt(pow(x[i]-x[j], 2) + pow(y[i]-y[j], 2));
      d = max<real>(0.0, d-r[i]-r[j]);
      dist[i][j] = dist[j][i] = d;
    }
  }

  vector<real> dd(n+2, 1e18);
  priority_queue<pair<real,int>, vector<pair<real,int>>, greater<pair<real,int>>> pq;
  dd[n] = 0.0;
  pq.push({dd[n], n});
  while(pq.size()){
    auto p = pq.top(); pq.pop();
    if(p.first > dd[p.second]) continue;
    for(auto i : range(n+2) ){
      if(i == p.second) continue;
      real nx = p.first + dist[p.second][i];
      if(nx < dd[i]){
        dd[i] = nx;
        pq.push({nx, i});
      }
    }
  }

  printf("%.16f\n", (double)dd[n+1]);

  return 0;
}


Measured memory_bytes: 24300