using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

// using System.Numerics;
using System.Runtime.CompilerServices;
using System.Diagnostics;
using ll=System.Int64;
using static Contest_C.Lib_IO;
using static Contest_C.Lib_Minifunc;



public static class Contest_C
{

	public static void Main() {
		checked{
			double  x1,y1,x2,y2;
			ll n;
			Lib_IO.rm(out x1, out y1,out x2, out y2);
			Lib_IO.rm(out n);
			P<double,double,double>[] xyr;
			rl(n,out xyr);

			List<P<ll,ll,double>> edge = new List<P<ll, ll, double>>();
			edge.Add(new P<ll, ll, double>(n,n+1,Math.Sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))));
			for (int i = 0; i < n; i++)
			{
				double xx = xyr[i].A-x2;
				double yy = xyr[i].B-y2;
				double d = max(Math.Sqrt(xx*xx+yy*yy)-xyr[i].C,0.0);
				edge.Add(new P<ll, ll, double>(i,n+1,d));
			}
			for (int i = 0; i < n; i++)
			{
				double xx = xyr[i].A-x1;
				double yy = xyr[i].B-y1;
				double d = max(Math.Sqrt(xx*xx+yy*yy)-xyr[i].C,0.0);
				edge.Add(new P<ll, ll, double>(n,i,d));
			}
			for (int i = 0; i < n-1; i++)
			{
				for (int j = i+1; j < n; j++)
				{
					double xx = xyr[i].A-xyr[j].A;
					double yy = xyr[i].B-xyr[j].B;
					double d = max(Math.Sqrt(xx*xx+yy*yy)-xyr[i].C-xyr[j].C,0.0);
					edge.Add(new P<ll, ll, double>(i,j,d));
				}
			}

			ll[] prev;
			var ans = Dijkstra(edge.ToArray(), n+2, n, out prev);

			Lib_IO.wm(ans[n+1]);
		}
	}


	public static long[] RestoreRoute(long[] prev, long end){
		var path = new List<long>();
		for(long u = end; u >= 0; u = prev[u]) path.Add(u);
		path.Reverse();
		return path.ToArray();
	}

	public static double[] Dijkstra(P<long,long,double>[] inEdges, long V, long start, out long[] prev) {
		double[] dist = Enumerable.Repeat((double)long.MaxValue, (int)V).ToArray();
		prev = Enumerable.Repeat(-1L, (int)V).ToArray();
		var G = new Dictionary<long,double>[V]; 
		for(int i=0;i<V;i++) G[i] = new Dictionary<long,double>();
		foreach(var e in inEdges){
			G[e.A][e.B] = e.C;
			G[e.B][e.A] = e.C;
		}

		var que = new PriorityQueue<KeyValuePair<double, long>>(V, (x,y)=>(x.Key.CompareTo(y.Key)));
		dist[start] = 0;
		que.Enqueue(new KeyValuePair<double, long>(dist[start], start));
		while(0<que.Count) {
			var q = que.Dequeue();
			if(dist[q.Value] < q.Key) continue;
			foreach(var e in G[q.Value]){
				var next_cost = q.Key + e.Value;
				if(dist[e.Key] <= next_cost) continue;
				dist[e.Key] = next_cost;
				que.Enqueue(new KeyValuePair<double, long>(dist[e.Key], e.Key));
			   	prev[e.Key] = q.Value;
			}
		}
		return dist;
	}
	

public class PriorityQueue<T>
{
	private readonly List<T> heap;
	private readonly Comparison<T> compare;
	private int size;
	public PriorityQueue() : this(Comparer<T>.Default) {} 
	public PriorityQueue(IComparer<T> comparer) : this(16, comparer.Compare) { }
	public PriorityQueue(Comparison<T> comparison) : this(16, comparison) { }
	public PriorityQueue(long capacity, Comparison<T> comparison)
	{
		this.heap = new List<T>((int)capacity);
		this.compare = comparison;
	}
	public void Enqueue(T item)
	{
		this.heap.Add(item);
		var i = size++;
		while (i > 0)
		{
			var p = (i - 1) >> 1;
			if (compare(this.heap[p], item) <= 0)
				break;
			this.heap[i] = heap[p];
			i = p;
		}
		this.heap[i] = item;

	}
	public T Dequeue()
	{
		var ret = this.heap[0];
		var x = this.heap[--size];
		var i = 0;
		while ((i << 1) + 1 < size)
		{
			var a = (i << 1) + 1;
			var b = (i << 1) + 2;
			if (b < size && compare(heap[b], heap[a]) < 0) a = b;
			if (compare(heap[a], x) >= 0)
				break;
			heap[i] = heap[a];
			i = a;
		}
		heap[i] = x;
		heap.RemoveAt(size);
		return ret;
	}
	public T Peek() { return heap[0]; }
	public long Count { get { return size; } }
	public bool Any() { return size > 0; }
}













#region BaseModule


public static class Lib_Minifunc{
	[MethodImpl(256)] public static void swap1<T>(ref T a, ref T b) { T t = a; a = b; b = t; }
	[MethodImpl(256)] public static void swap2<T>(ref T a, ref T b) where T : IComparable { if (a.CompareTo(b)==1) swap1(ref a, ref b); }  // b の方が小さければ交換
	[MethodImpl(256)] public static bool chmin<T>(ref T a, T b) where T : IComparable { if (a.CompareTo(b)== 1) { a = b; return true; } return false; }  // b の方が小さければ a を更新
	[MethodImpl(256)] public static bool chmax<T>(ref T a, T b) where T : IComparable { if (a.CompareTo(b)==-1) { a = b; return true; } return false; }  // b の方が大きければ a を更新
	[MethodImpl(256)] public static bool inside(long i, long n) => (0<=i&&i<n);
	[MethodImpl(256)] public static bool inside(long x, long y, long w, long h) => (inside(x,w)&&inside(y,h));
	[MethodImpl(256)] public static T min<T>(params T[] a) where T : IComparable => a.Min();
	[MethodImpl(256)] public static T max<T>(params T[] a) where T : IComparable => a.Max();
	[MethodImpl(256)] public static long mod(long a, long m=MOD1) { var v = a%m; return (v<0?v+m:v); }
	[MethodImpl(256)] public static long ceiling(long a, long b) => (a%b==0?a/b:a/b+1);	// 整数商の切り上げ
	[MethodImpl(256)] public static P<T,U> initp<T,U>(T a,U b) => new P<T,U>(a,b);
	[MethodImpl(256)] public static P<T,U,V> initp<T,U,V>(T a,U b,V c) => new P<T,U,V>(a,b,c);
	[MethodImpl(256)] public static P<T,U,V,W> initp<T,U,V,W>(T a,U b,V c,W d) => new P<T,U,V,W>(a,b,c,d);
	[MethodImpl(256)] public static bool initd<T,U>(Dictionary<T,U> d, T k) { if(d.ContainsKey(k)) { return false; } else { d[k] = default(U); return true; } }
	public static T[] inita<T>(long len1) where T : new() { var m = new T[len1]; for (int i=0;i<m.Length;i++) m[i] = new T(); return m; }
	public static T[][] initm<T>(long len1,long len2,T val) where T : struct { var m = new T[len1][]; for (int i=0;i<m.Length;i++) m[i] = Enumerable.Repeat(val,(int)len2).ToArray(); return m; }
	public static T[][][] initm<T>(long len1,long len2,long len3,T val) where T : struct { var m = new T[len1][][]; for (int i=0;i<m.Length;i++) m[i] = initm(len2,len3,val); return m; }
	public const long MOD1 = 1000000007; // 10^9+7
	public const double EPS1 = 1e-8;
	public const long INF1 = 1000000000000000;  // 10^15
}

public struct P<T,U>
{
	public T A; public U B;
	public P(T a,U b) { A = a; B = b; }
	public static implicit operator KeyValuePair<T,U>(P<T,U> a) => new KeyValuePair<T,U>(a.A,a.B);
	public static implicit operator P<T,U>(KeyValuePair<T,U> a) => new P<T,U>(a.Key,a.Value);
}
public struct P<T,U,V>
{
	public T A; public U B; public V C;
	public P(T a,U b,V c) { A = a; B = b; C = c; }
}
public struct P<T,U,V,W>
{
	public T A; public U B; public V C; public W D;
	public P(T a,U b,V c,W d) { A = a; B = b; C = c; D = d; }
}

public static class Lib_IO
{
	class Prt : System.IO.StreamWriter
	{
		public override IFormatProvider FormatProvider { get { return System.Globalization.CultureInfo.InvariantCulture; } }
		public Prt(System.IO.Stream s) : base(s,new UTF8Encoding(false,true)) {}
		public Prt(System.IO.Stream s,Encoding e) : base(s,e) {}
	}
	static Prt sw = new Prt(Console.OpenStandardOutput());
	static char[] sp = new char[] {' '};
	[MethodImpl(256)] static bool eq<T,U>() => typeof(T).Equals(typeof(U));
	[MethodImpl(256)] static T ct<T,U>(U a) => (T)Convert.ChangeType(a,typeof(T));
	[MethodImpl(256)] static T cv<T>(string s) =>
		eq<T,int>()	? ct<T,int>(int.Parse(s))
	  : eq<T,long>()   ? ct<T,long>(long.Parse(s))
	  : eq<T,double>() ? ct<T,double>(double.Parse(s,System.Globalization.CultureInfo.InvariantCulture))
	  : eq<T,char>()   ? ct<T,char>(s[0])
					   : ct<T,string>(s);
	public static string[] rm<T>(out T a) {
		var z = Console.ReadLine().Split(sp,StringSplitOptions.RemoveEmptyEntries); 
		a = cv<T>(z[0]);
		return z;
	}
	public static string[] rm<T,U>(out T a,out U b) {
		var z = rm<T>(out a); 
		b = cv<U>(z[1]);
		return z;
	}
	public static string[] rm<T,U,V>(out T a,out U b,out V c) {
		var z = rm<T,U>(out a,out b); 
		c = cv<V>(z[2]);
		return z;
	}
	public static string[] rm<T,U,V,W>(out T a,out U b,out V c,out W d) {
		var z = rm<T,U,V>(out a,out b,out c); 
		d = cv<W>(z[3]);
		return z;
	}
	public static string[] rm<T,U,V,W,X>(out T a,out U b,out V c,out W d,out X e) {
		var z = rm<T,U,V,W>(out a,out b,out c,out d); 
		e = cv<X>(z[4]);
		return z;
	}
	public static string[] rm<T,U,V,W,X,Y>(out T a,out U b,out V c,out W d,out X e,out Y f) {
		var z = rm<T,U,V,W,X>(out a,out b,out c,out d,out e); 
		f = cv<Y>(z[5]);
		return z;
	}
	public static string[] ra<T>(out T[] a) {		
		var z = Console.ReadLine().Split(sp,StringSplitOptions.RemoveEmptyEntries);
		a = z.Select(cv<T>).ToArray();
		return z;
	}
	public static string[][] rl<T>(long n,out T[] a) {
		a = new T[n];
		var y = new string[n][];
		for(int i=0;i<n;i++) y[i] = rm(out a[i]);
		return y;
	}
	public static string[][] rl<T,U>(long n,out P<T,U>[] a) {
		a = new P<T,U>[n];
		var y = new string[n][];
		for(int i=0;i<n;i++) {
			T o; U p;
			y[i] = rm(out o,out p);
			a[i] = new P<T,U>(o,p);
		}
		return y;
	}
	public static string[][] rl<T,U,V>(long n,out P<T,U,V>[] a) {
		a = new P<T,U,V>[n];
		var y = new string[n][];
		for(int i=0;i<n;i++) {
			T o; U p; V q;
			y[i] = rm(out o,out p,out q);
			a[i] = new P<T,U,V>(o,p,q);
		}
		return y;
	}
	public static string[][] rl<T,U,V,W>(long n,out P<T,U,V,W>[] a) {
		a = new P<T,U,V,W>[n];
		var y = new string[n][];
		for(int i=0;i<n;i++) {
			T o; U p; V q; W r;
			y[i] = rm(out o,out p,out q,out r);
			a[i] = new P<T,U,V,W>(o,p,q,r);
		}
		return y;
	}
	public static string[][] rx<T>(long n,out T[][] a) {
		a = new T[n][];
		var y = new string[n][];
		for(int i=0;i<n;i++) y[i] = ra(out a[i]);
		return y;
	}

	static void wwp(Action act){
		sw.AutoFlush = false;
		Console.SetOut(sw);
		act();
		Console.Out.Flush();
		sw.AutoFlush = true;
		Console.SetOut(sw);
	}
	[MethodImpl(256)] static string wfm(Type t) =>t.Equals(typeof(double)) ? "{0:F10}" : "{0}";
	public static void wm(params object[] a) {
		wwp(()=>{
			for(int i=0;i<a.Length-1;i++) Console.Write(wfm(a[i].GetType())+" ",a[i]);
			Console.WriteLine(wfm(a[a.Length-1].GetType()),a[a.Length-1]);
		});
	}
	public static void wa<T>(IList<T> a) { wxa(new IList<T>[]{a}, " "); }
	public static void wl<T>(IList<T> a) {
		wwp(()=>{
			var f = wfm(typeof(T));
			foreach(T x in a) Console.WriteLine(f,x);
		});
	}
	static void wxa<T>(IList<IList<T>> a, string s) {
		wwp(()=>{
			var f = wfm(typeof(T));
			var g = f + s;
			foreach(var b in a) {
				for(int i=0;i<b.Count-1;i++) Console.Write(g,b[i]);
				Console.WriteLine(f,b[b.Count-1]);
			}
		});
	}
	public static void wx<T>(IList<IList<T>> a) { wxa(a, " "); }
	public static void wg<T>(IList<IList<T>> a) { wxa(a, ""); }
}

#endregion



}



Measured memory_bytes: 120100