#include <bits/stdc++.h>
            #include<iostream>
            #include<cstdio>
            #include<vector>
            #include<queue>
            #include<map>
            #include<cstring>
            #include<string>
            #include <math.h>
            #include<algorithm>
        //    #include <boost/multiprecision/cpp_int.hpp>
            #include<functional>
          #define int long long
            #define inf  1000000007
            #define pa pair<int,int>
    #define ll long long
            #define pal pair<double,int>
            #define ppa pair<int,pa>
             #define ssa pair<string,int>
            #define  mp make_pair
            #define  pb push_back
            #define EPS (1e-10)
            #define equals(a,b) (fabs((a)-(b))<EPS)
     
            using namespace std;
     
            class Point{
            	public:
            	double x,y;
            	Point(double x=0,double y=0):x(x),y(y) {}
            	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
            	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
            	Point operator * (double a) {return Point(x*a,y*a);}
            	Point operator / (double a) {return Point(x/a,y/a);}
            	double absv() {return sqrt(norm());}
            	double norm() {return x*x+y*y;}
            	bool operator < (const Point &p) const{
            		return x != p.x ? x<p.x: y<p.y;
            	}
            	bool operator == (const Point &p) const{
            		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
            	}
            };
            typedef Point Vector;
     
            struct Segment{
            Point p1,p2;
            };
     
        double hen(Vector a){
        if(fabs(a.x)<EPS && a.y>0) return acos(0);
        else if(fabs(a.x)<EPS && a.y<0) return 3*acos(0);
        else if(fabs(a.y)<EPS && a.x<0) return 2*acos(0);
        else if(fabs(a.y)<EPS && a.x>0) return 0.0;
        else if(a.y>0) return acos(a.x/a.absv());
        else return 2*acos(0)+acos(-a.x/a.absv());
     
        }
     
int gcd(int v,int b){
	if(v>b) return gcd(b,v);
	if(v==b) return b;
	if(b%v==0) return v;
	return gcd(v,b%v);
}
            double dot(Vector a,Vector b){
            	return a.x*b.x+a.y*b.y;
            }
            double cross(Vector a,Vector b){
            	return a.x*b.y-a.y*b.x;
            }
        
            //----------------kokomade tenpure------------
double xs,xt,ys,yt,x,y,r;
double xx[1002],yy[1002],rr[1002];
//vector<pal> G[1005];
double G[1005][1005];


double kyori(double xxs,double yys,double xxt,double yyt ){
	double c=(xxs-xxt)*(xxs-xxt) +(yys-yyt)*(yys-yyt);
	return sqrt(c);
	
}

int n;

priority_queue<pal, vector<pal>, greater<pal> > pq;
    signed  main(){
cin>>xx[0]>>yy[0]>>xt>>yt;
    	cin>>n;
    	xx[n+1]=xt;
    	yy[n+1]=yt;
    	for(int i=1;i<=n;i++){
    		cin>>xx[i]>>yy[i]>>rr[i];
    		
    	}
    	for(int i=0;i<=n+1;i++){
    		G[i][i]=0.0;
    		for(int j=i+1;j<=n+1;j++){
    			G[i][j] =kyori(xx[i],yy[i],xx[j],yy[j])- rr[i]-rr[j];
    			if(G[i][j]<0) G[i][j]=0.0;
    			G[j][i]=G[i][j];
    			
    		}
    	}
    	
    	bool sumi[1004]={0};
    	sumi[0]=1;
    	double ky[1004];
    	for(int i=1;i<=n+1;i++){
    		pq.push(mp(G[0][i],i));
    	}
    	ky[0]=0.0;
    	while(pq.size()>0){
    		pal z;
    		if(sumi[n+1]==1) break;
    		while(1){
    		z=pq.top();
    		pq.pop();
    			if(sumi[z.second]==0) break;
    		}
    		sumi[z.second]=1;
    		ky[z.second]= z.first;
    		for(int i=0;i<=n+1;i++){
    			if(sumi[i]==1) continue;
    			pq.push(mp(G[z.second][i]+z.first,i));
    		}
    		
    		if(sumi[n+1]==1) break;
    	}
    	
    	
    	
    	printf("%.10f\n",ky[n+1]);
    	return 0;
    }

Measured memory_bytes: 16492