#include "bits/stdc++.h"
using namespace std;
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define oorret 0
#define oor(x) [&](){try{x;} catch(const out_of_range& oor){return oorret;} return x;}()
#define IOS cin.tie(0),ios::sync_with_stdio(false)
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
template<class Type>struct is_vector : std::false_type {};
template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
template <typename T> inline ostream& operator << (ostream& out, const vector<T>& v) {
    if (v.empty())return out;
    constexpr bool is_vector_v = is_vector<T>::value;
    if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? "\n" : "");
    else for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? " " : "");
    return out;
}
inline void put() {}
template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }
inline void putn() {}
template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first << "\n"; putn(rest...); }

template<typename T>
struct edge{
    int to;
    T cost;
    edge(int t,T c){
        to = t;
        cost = c;
    }
};

template<typename T>
void dijkstra(int s,vector<vector<edge<T>>>& path,vector<T>& d){
    using pi = pair<T,int>;
    priority_queue<pi,vector<pi>,greater<pi>> q;
    q.push(P(0,s));
    d[s] = 0;
    while(!q.empty()){
        P p = q.top();
        q.pop();
        int v = p.second;
        if(d[v]<p.first)continue;
        REP(i,path[v].size()){
            edge<T> e = path[v][i];
            if(d[e.to]>d[v]+e.cost){
                d[e.to]=d[v]+e.cost;
                q.push(P(d[e.to],e.to));
            }
        }
    }
    return ;
}

int main() {
    IOS;
    ll xs,ys,xt,yt;
    cin >> xs >> ys >> xt >> yt;
    int n;
    cin >> n;
    vector<ll> x(n+2),y(n+2),r(n+2);
    using ld = long double;
    vector<vector<edge<ld>>> path(n+2);
    REP(i,n){
        cin >> x[i] >> y[i] >> r[i];
    }
    x[n] = xs;
    y[n] = ys;
    r[n] = 0;
    x[n+1] = xt;
    y[n+1] = yt;
    r[n+1] = 0;
    REP(i,n+2){
        REP(j,n+2){
            ld dist = max<ld>(sqrt((ld)(x[i]-x[j])*(x[i]-x[j])+(ld)(y[i]-y[j])*(y[i]-y[j]))-r[i]-r[j],0);
            path[i].push_back(edge<ld>(j,dist));
        }
    }
    vector<ld> d(n+2,1e15);
    dijkstra(n, path, d);
    cout << setprecision(20) << d[n+1] << endl;
    return 0;
}


Measured memory_bytes: 42348