#include<bits/stdc++.h>
using namespace std;
#define sync ios_base::sync_with_stdio(false), cin.tie(NULL)
#define F first
#define S second
#define pb emplace_back
#define mt make_tuple
#define gcd __gcd
#define PI 3.141592653589
// Input
#define in(a) scanf("%d",&a)
#define in2(a,b) scanf("%d%d",&a,&b)
#define in3(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define llin(a) cin >> a
#define inl(a) scanf("%lld",&a)
#define read(v,i,n) for(i=0;i<n;i++)in(v[i])
#define twod(mat,i,j,n,m) rep(i,n){rep(j,m)in(mat[i][j]);}
#define sc(ch) scanf("%c",&ch)
#define sstr(str) scanf("%s",str)
// Output
#define pr(a) printf("%d ",a)
#define pr2(a,b) printf("%d %d\n",a,b)
#define pr3(a,b,c) printf("%d %d %d\n",a,b,c)
#define out(a) printf("%d\n",a)
#define outl(a) printf("%lld\n",a)
#define llpr(a) cout << a << " "
#define llout(a) cout << a << "\n"
#define yes printf("YES\n")
#define no printf("NO\n")
#define lin printf("\n")
// Iterator
#define lp(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) for(i=0;i<n;i++)
#define all(vec) vec.begin(),vec.end()
#define lower(v,k) lower_bound(v.begin(),v.end(),k)-v.begin()
#define upper(v,k) upper_bound(v.begin(),v.end(),k)-v.begin()
#define tf(mytuple) get<0>(mytuple)
#define ts(mytuple) get<1>(mytuple)
#define tt(mytuple) get<2>(mytuple)
// Debug
#define dbg(v,i,n) for(i=0;i<n;i++)pr(v[i]); lin
#define what(x) cerr << #x << " : " << x << "\n"
#define ck printf("continue\n")
#define debug(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args)
{
	cerr << *it << " = " << a << "\n";
	err(++it, args...);
}
// Data Type
#define ll long long int
#define ii pair<int,int>
//#define pli pair<ll,int>
#define triple tuple<int,int,int>
#define vi vector<int>
#define vii vector<pair<int,int> >
#define vvi vector<vector<int> >
#define viii vector<pair<pair<int,int>,int> >
#define vvii vector<vector<pair<int,int> > >
#define M 1000000007
#define N 1005  //check the limits, man
const ll INF = 1e12;
long double ad[N][N];
long double calc(triple A,triple B)
{
    ll p,q;
    p=tf(A)-tf(B),p*=p;
    q=ts(A)-ts(B),q*=q;
    long double d;
    d=p+q;
    d=sqrt(d);
    return max(d-d,d-tt(A)-tt(B));
}
long double dis[N];
bool vis[N];
#define pli pair<long double,int>
void dijkstra(int s,int n)
{
    int a,i,x;
    long double c;
    fill(dis,dis+n,INF);
    dis[s]=0;
    priority_queue<pli,vector<pli>,greater<pli> > pq;
    pq.push({0,s});
    pli temp;
    while(!pq.empty())
    {
        temp=pq.top();
        pq.pop();
        s=temp.S;
        if(!vis[s])
        {
            vis[s]=1;
            rep(i,n)
            {
                a=i,c=ad[s][i];
                if(!vis[a] && dis[a]>dis[s]+c)
                    dis[a]=dis[s]+c,pq.push({dis[a],a});
            }
        }
    }
    return ;
}
int main()
{
    int a,b,x,y,n,i,j,c;
    in2(a,b);
    in2(x,y);
    in(n);
    vector<triple> v(n+2);
    v[0]=mt(a,b,0);
    v[n+1]=mt(x,y,0);
    lp(i,1,n+1)
    {
        in3(a,b,c);
        v[i]=mt(a,b,c);
    }
    n+=2;
    cout << setprecision(15) << fixed;
    rep(i,n)
    {
        rep(j,n)
        {
            ad[i][j]=calc(v[i],v[j]);
        }
    }
    dijkstra(0,n);
    llout(dis[n-1]);
}



Measured memory_bytes: 26224