#include <iostream>
#include <algorithm>
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
#include <string.h>
#include <numeric>
using namespace std;

//#define int long long
#define reps(i,s,n) for(int (i)=(s);(i)<(n);++(i))
#define rep(i,n) reps(i,0,n)
#define rept(i,n) rep(i,(n)+1)
#define repst(i,s,n) reps(i,s,(n)+1)
#define reprt(i,n,t) for(int (i)=(n);(i)>=(t);--(i))
#define repr(i,n) reprt(i,n,0)
#define each(i,v) for(auto &(i):(v))
#define eachr(i,v) for(auto &(i)=(v).rbegin();(i)!=(v).rend();(i)++)
#define all(c) (c).begin(),(c).end()
#define rall(c) (c).rbegin(),(c).rend()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define tmax(x,y,z) max(x,max(y,z))
#define tmin(x,y,z) min(x,min(y,z))
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
#define ln '\n'
#define bln(i,n) (((i)==(n)-1)?'\n':' ')
#define dbg(x) cout<<#x" = "<<(x)<<ln<<flush
#define dbga(x,n) {cout<<#x" : ";for(int (i)=0;i<(n);++i){cout<<((x)[i])<<(i==((n)-1)?'\n':' ')<<flush;}}
#define zero(a) memset(a,0,sizeof(a))
#define unq(a) sort(all(a)),a.erase(unique(all(a)),a.end())

//typedef complex<double> P;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<string> vst;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<vector<int> > mat;

const ll inf = (ll)1e9+10;
const ll linf = (ll)1e18+10;
const ll mod = (ll)(1e9+7);
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
const int ddx[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int ddy[] = {1, 1, 0, -1, -1, -1, 0, 1};
const double eps = 1e-10;

ll mop(ll a,ll b,ll m=mod) {ll r=1;a%=m;for(;b;b>>=1){if(b&1)r=r*a%m;a=a*a%m;}return r;}
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b) {return a/gcd(a,b)*b;}
bool ool(int x,int y,int h,int w) {return((x<0)||(h<=x)||(y<0)||(w<=y));}
bool deq(double a,double b) {return abs(a-b)<eps;}

struct oreno_initializer {
	oreno_initializer() {
		cin.tie(0);
		ios::sync_with_stdio(0);
	}
} oreno_initializer;



int n;
double x[1010], y[1010], r[1010], d[1010];
vector<pair<int,double> > e[1010];

void dijkstra(int n, vector<pair<int,double>> e[], double d[], int s) {
	priority_queue<pair<int,double>, vector<pair<int,double>>, greater<pair<int,double>>> que;
	fill(d, d+n, 1e100), d[s] = 0;
	que.push({0,s});
	while(!que.empty()) {
		int v = que.top().second;
		double dis = que.top().first;
		que.pop();
		if (d[v]<dis) continue;
		for (int i = 0; i < e[v].size(); ++i) {
			int to = e[v][i].first;
			double cost = e[v][i].second;
			if (d[to] > d[v] + cost) {
				d[to] = d[v] + cost;
				que.push({d[to], to});
			}
		}
	}
}

signed main() {
	cin >> x[0] >> y[0] >> x[1005] >> y[1005] >> n;
	n += 2;
	x[n-1] = x[1005], y[n-1] = y[1005];
	reps(i,1,n-1) cin >> x[i] >> y[i] >> r[i];
	rep(i,n) reps(j,i+1,n) {
		double dis = sqrt((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));
		dis = max(0., dis-(r[i]+r[j]));
		e[i].push_back({j,dis}), e[j].push_back({i,dis});
	}
	dijkstra(n,e,d,0);
	printf("%.14lf\n",d[n-1]);
}

Measured memory_bytes: 22660