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

#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define lfs <<fixed<<setprecision(10)<<
#define test cout<<"test"<<endl;
#define fi first
#define se second
#define MP make_pair
#define rep(i,n,m) for(ll i = n; i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = n - 1; i >= (ll)(m); i--)
typedef long long ll;
typedef long double ld;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const ll INF = 1e18;
template<typename T>
void chmin(T &a,T b){if(a>b)a=b;}
template<typename T>
void chmax(T &a,T b){if(a<b)a=b;}
void pmod(ll &a,ll b){a=(a+b)%MOD;}
void pmod(ll &a,ll b,ll c){a=(b+c)%MOD;}
void qmod(ll &a,ll b){a=(a*b)%MOD;}
void qmod(ll &a,ll b,ll c){a=(b*c)%MOD;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>
void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>
void debug(vector<vector<T>>v,ll h,ll w){for(ll i=0;i<h;i++)
{cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>v,ll h,ll w){for(ll i=0;i<h;i++)
{for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>
void debug(vector<T>v,ll n){cout<<v[0];
for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>
vector<vector<T>>vec(ll x, ll y, T w){
  vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
template<typename T>
void emp(map<T,ll>&m, T x){m.emplace(x,0).first->second++;}

//d[i]に始点からiまでの最短距離を出力

using P = pair<ld, ll>;
ll MAX_V = 1e3 + 5;
struct edge {
  ll to;
  ld cost;
  edge(ll x,ld y):to(x),cost(y){};
};

//<最短距離, 頂点の番号>using P = pair<ll, ll>;
vector<vector<struct edge>> G(MAX_V); //隣接リスト
vector<ld> d(MAX_V); //各頂点への最短距離
void dijkstra(ll s) {
    priority_queue<P, vector<P>, greater<P> > que;
    fill(ALL(d), INF);
    d[s] = 0;
    que.push(P(0, s));
    while (!que.empty()) {
        P p = que.top();
        que.pop();
        ll v = p.second;
        if (d[v] < p.first) continue;

        for (ll i=0; i<G[v].size(); i++) {
            struct edge e = G[v][i];
            if (d[e.to] > d[v] + e.cost) {
                d[e.to] = d[v] + e.cost;
                que.push(P(d[e.to], e.to));
            }
        }
    }
}


typedef struct circle{
  complex<ld>c;
  ld r;
}cir;
int main(){
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);
  ll res=0,res1=INF,res2=-INF,buf=0;
  bool judge = true;
  ld xs,ys,xt,yt;
  ll n;
  cin>>xs>>ys>>xt>>yt>>n;
  vector<cir>v(n+2);
  v[0]={{xs,ys},0};
  v[n+1]={{xt,yt},0};
  rep(i,1,n+1){
    ld x,y;
    cin>>x>>y>>v[i].r;
    v[i].c={x,y};
  }
  //for(auto z:v)cout<<z.c spa z.r<<endl;
  ld eps=1e-14;
  rep(i,0,n+2){
    rep(j,0,n+2){
      if(i!=j){
        complex<ld> dx=v[i].c-v[j].c;
        ld d=abs(dx);
        //cout<<dx spa d<<endl;
        if(d<=v[i].r+v[j].r+eps){
          G[i].emplace_back(j,0);
        }
        else G[i].emplace_back(j,d-v[i].r-v[j].r);
      }
    }
  }
  dijkstra(0);
  cout lfs d[n+1]<<endl;
  return 0;
}

Measured memory_bytes: 42732