#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, ll> pil;
typedef pair<ll, int> pli;
typedef pair<int, double> pid;
typedef pair<double, int> pdi;
typedef pair<double,double> pdd;
#define SQ(i) ((i)*(i))
#define MEM(a, b) memset(a, (b), sizeof(a))
#define SZ(i) int(i.size())
#define FOR(i, j, k, in) for (int i=j ; i<k ; i+=in)
#define RFOR(i, j, k, in) for (int i=j ; i>=k ; i-=in)
#define REP(i, j) FOR(i, 0, j, 1)
#define REP1(i,j) FOR(i, 1, j+1, 1)
#define RREP(i, j) RFOR(i, j, 0, 1)
#define ALL(_a) _a.begin(),_a.end()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define X first
#define Y second
#ifdef tmd
#define TIME(i) Timer i(#i)
#define debug(...) do{\
    fprintf(stderr,"%s - %d (%s) = ",__PRETTY_FUNCTION__,__LINE__,#__VA_ARGS__);\
    _do(__VA_ARGS__);\
}while(0)
template<typename T>void _do(T &&_x){cerr<<_x<<endl;}
template<typename T,typename ...S> void _do(T &&_x,S &&..._t){cerr<<_x<<" ,";_do(_t...);}
template<typename _a,typename _b> ostream& operator << (ostream &_s,const pair<_a,_b> &_p){return _s<<"("<<_p.X<<","<<_p.Y<<")";}
template<typename It> ostream& _OUTC(ostream &_s,It _ita,It _itb)
{
    _s<<"{";
    for(It _it=_ita;_it!=_itb;_it++)
    {
        _s<<(_it==_ita?"":",")<<*_it;
    }
    _s<<"}";
    return _s;
}
template<typename _a> ostream &operator << (ostream &_s,vector<_a> &_c){return _OUTC(_s,ALL(_c));}
template<typename _a> ostream &operator << (ostream &_s,set<_a> &_c){return _OUTC(_s,ALL(_c));}
template<typename _a> ostream &operator << (ostream &_s,deque<_a> &_c){return _OUTC(_s,ALL(_c));}
template<typename _a,typename _b> ostream &operator << (ostream &_s,map<_a,_b> &_c){return _OUTC(_s,ALL(_c));}
template<typename _t> void pary(_t _a,_t _b){_OUTC(cerr,_a,_b);cerr<<endl;}
#define IOS()
#else
#define TIME(i)
#define debug(...)
#define pary(...)
#define endl '\n'
#define IOS() ios_base::sync_with_stdio(0);cin.tie(0)
#endif
class Timer {
private:
    string scope_name;
    chrono::high_resolution_clock::time_point start_time;
public:
    Timer (string name) : scope_name(name) {
        start_time = chrono::high_resolution_clock::now();
    }
    ~Timer () {
        auto stop_time = chrono::high_resolution_clock::now();
        auto length = chrono::duration_cast<chrono::microseconds>(stop_time - start_time).count();
        double mlength = double(length) * 0.001;
        debug(scope_name, mlength);
    }
};

const ll MOD = 1000000007;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int iNF = 0x3f3f3f3f;
const ll MAXN = 1003;

pii p[MAXN];
int r[MAXN], n;
double dis[MAXN];
bool vis[MAXN];

vector<pid> edge[MAXN];
/********** Good Luck  **********/
int main()
{
    TIME(main);
    IOS();

    cin >> p[0].X >> p[0].Y >> p[MAXN-1].X >> p[MAXN-1].Y;
    cin >> n;


    REP1 (i, n) {
        cin >> p[i].X >> p[i].Y >> r[i];
    }
    n++;
    p[n] = p[MAXN - 1];

    REP (i, n + 1) {
        REP (j, n + 1) {
            edge[i].eb(j, max(0.0, sqrt(SQ(ll(p[i].X - p[j].X)) + SQ(ll(p[i].Y - p[j].Y))) - r[i] - r[j]));
        }
    }

    priority_queue<pdi, vector<pdi>, greater<pdi> > pq;
    pq.emplace(0, 0);

    REP1 (i, n) {
        dis[i] = 1e17;
    }

    REP (i, n + 1) {
        int fnd = -1;
        while (pq.size() && vis[fnd = pq.top().Y]) {
            pq.pop();
        }
        assert(fnd != -1);
        vis[fnd] = true;

        for (auto e : edge[fnd]) {
            if (dis[e.X] > dis[fnd] + e.Y) {
                dis[e.X] = dis[fnd] + e.Y;
                pq.emplace(dis[e.X], e.X);
            }
        }
    }

    cout << fixed << setprecision(16) << dis[n] << endl;
    return 0;
}


Measured memory_bytes: 22128