using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using static System.Math;
using System.Text;
using System.Threading;
using System.Globalization;
using System.Runtime.CompilerServices;
using Library;

namespace Program
{
    public static class ProblemA
    {
        static bool SAIKI = false;
        static public int numberOfRandomCases = 0;
        static public void MakeTestCase(List<string> _input, List<string> _output, ref Func<string[], bool> _outputChecker)
        {
        }
        static public void Solve()
        {
            var xs = NN;
            var ys = NN;
            var xt = NN;
            var yt = NN;
            var N = NN;
            var xyr = Repeat(0, N).Select(_ => new { x = NN, y = NN, r = NN }).ToArray();
            var path = Repeat(0, N + 2).Select(_ => new List<Tuple<long, double>>()).ToArray();
            for (var i = 0; i < N; i++)
            {
                for (var j = i + 1; j < N; j++)
                {
                    var p1 = new LIB_Geo2D.Vec(xyr[i].x, xyr[i].y);
                    var p2 = new LIB_Geo2D.Vec(xyr[j].x, xyr[j].y);
                    var dist = Sqrt(LIB_Geo2D.Distance(p1, p2)) - xyr[i].r - xyr[j].r;
                    if (dist < LIB_Geo2D.EPS) dist = 0;
                    path[i].Add(Tuple.Create((long)j, dist));
                    path[j].Add(Tuple.Create((long)i, dist));
                }
            }
            for (var j = 0; j < N; j++)
            {
                var p1 = new LIB_Geo2D.Vec(xs, ys);
                var p2 = new LIB_Geo2D.Vec(xyr[j].x, xyr[j].y);
                var dist = Sqrt(LIB_Geo2D.Distance(p1, p2)) - xyr[j].r;
                if (dist < LIB_Geo2D.EPS) dist = 0;
                path[N].Add(Tuple.Create((long)j, dist));
                path[j].Add(Tuple.Create((long)N, dist));
            }
            for (var j = 0; j < N; j++)
            {
                var p1 = new LIB_Geo2D.Vec(xt, yt);
                var p2 = new LIB_Geo2D.Vec(xyr[j].x, xyr[j].y);
                var dist = Sqrt(LIB_Geo2D.Distance(p1, p2)) - xyr[j].r;
                if (dist < LIB_Geo2D.EPS) dist = 0;
                path[N + 1].Add(Tuple.Create((long)j, dist));
                path[j].Add(Tuple.Create((long)N + 1, dist));
            }
            {
                var p1 = new LIB_Geo2D.Vec(xt, yt);
                var p2 = new LIB_Geo2D.Vec(xs, ys);
                var dist = Sqrt(LIB_Geo2D.Distance(p1, p2));
                if (dist < LIB_Geo2D.EPS) dist = 0;
                path[N + 1].Add(Tuple.Create((long)N, dist));
                path[N].Add(Tuple.Create((long)N + 1, dist));
            }
            {
                var nodeNum = N + 2;
                var start = N;
                var dist = Repeat(double.MaxValue / 4, nodeNum).ToArray();
                dist[start] = 0;
                var close = new bool[nodeNum];
                while (true)
                {
                    var minDist = double.MaxValue / 4; // !!!
                    var minVtx = -1;
                    for (var k = 0; k < nodeNum; k++)
                    {
                        if (!close[k])
                        {
                            if (minDist > dist[k]) // !!!
                            {
                                minDist = dist[k];
                                minVtx = k;
                            }
                        }
                    }
                    if (minVtx == -1) break;
                    close[minVtx] = true;
                    foreach (var item in path[minVtx])
                    {
                        var distTemp = dist[minVtx] + item.Item2; // !!!
                        if (dist[item.Item1] > distTemp) // !!!
                        {
                            dist[item.Item1] = distTemp;
                        }
                    }
                }
                Console.WriteLine(dist[N + 1]);
            }
        }
        class Printer : StreamWriter
        {
            public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
            public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { base.AutoFlush = false; }
            public Printer(Stream stream, Encoding encoding) : base(stream, encoding) { base.AutoFlush = false; }
        }
        static LIB_FastIO fastio = new LIB_FastIODebug();
        static public void Main(string[] args) { if (args.Length == 0) { fastio = new LIB_FastIO(); Console.SetOut(new Printer(Console.OpenStandardOutput())); } if (SAIKI) { var t = new Thread(Solve, 134217728); t.Start(); t.Join(); } else Solve(); Console.Out.Flush(); }
        static long NN => fastio.Long();
        static double ND => fastio.Double();
        static string NS => fastio.Scan();
        static long[] NNList(long N) => Repeat(0, N).Select(_ => NN).ToArray();
        static double[] NDList(long N) => Repeat(0, N).Select(_ => ND).ToArray();
        static string[] NSList(long N) => Repeat(0, N).Select(_ => NS).ToArray();
        static long Count<T>(this IEnumerable<T> x, Func<T, bool> pred) => Enumerable.Count(x, pred);
        static IEnumerable<T> Repeat<T>(T v, long n) => Enumerable.Repeat<T>(v, (int)n);
        static IEnumerable<int> Range(long s, long c) => Enumerable.Range((int)s, (int)c);
        static IOrderedEnumerable<T> OrderByRand<T>(this IEnumerable<T> x) => Enumerable.OrderBy(x, _ => xorshift);
        static IOrderedEnumerable<T> OrderBy<T>(this IEnumerable<T> x) => Enumerable.OrderBy(x.OrderByRand(), e => e);
        static IOrderedEnumerable<T1> OrderBy<T1, T2>(this IEnumerable<T1> x, Func<T1, T2> selector) => Enumerable.OrderBy(x.OrderByRand(), selector);
        static IOrderedEnumerable<T> OrderByDescending<T>(this IEnumerable<T> x) => Enumerable.OrderByDescending(x.OrderByRand(), e => e);
        static IOrderedEnumerable<T1> OrderByDescending<T1, T2>(this IEnumerable<T1> x, Func<T1, T2> selector) => Enumerable.OrderByDescending(x.OrderByRand(), selector);
        static IOrderedEnumerable<string> OrderBy(this IEnumerable<string> x) => x.OrderByRand().OrderBy(e => e, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<T> OrderBy<T>(this IEnumerable<T> x, Func<T, string> selector) => x.OrderByRand().OrderBy(selector, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<string> OrderByDescending(this IEnumerable<string> x) => x.OrderByRand().OrderByDescending(e => e, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<T> OrderByDescending<T>(this IEnumerable<T> x, Func<T, string> selector) => x.OrderByRand().OrderByDescending(selector, StringComparer.OrdinalIgnoreCase);
        static uint xorshift { get { _xsi.MoveNext(); return _xsi.Current; } }
        static IEnumerator<uint> _xsi = _xsc();
        static IEnumerator<uint> _xsc() { uint x = 123456789, y = 362436069, z = 521288629, w = (uint)(DateTime.Now.Ticks & 0xffffffff); while (true) { var t = x ^ (x << 11); x = y; y = z; z = w; w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)); yield return w; } }
    }
}
namespace Library {
    class LIB_FastIO
    {
        public LIB_FastIO() { str = Console.OpenStandardInput(); }
        readonly Stream str;
        readonly byte[] buf = new byte[1024];
        int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        byte read()
        {
            if (isEof) throw new EndOfStreamException();
            if (ptr >= len)
            {
                ptr = 0;
                if ((len = str.Read(buf, 0, 1024)) <= 0)
                {
                    isEof = true;
                    return 0;
                }
            }
            return buf[ptr++];
        }
        char Char()
        {
            byte b = 0;
            do b = read();
            while (b < 33 || 126 < b);
            return (char)b;
        }
        virtual public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        virtual public long Long()
        {
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != '-' && (b < '0' || '9' < b));
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        virtual public double Double() { return double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
    class LIB_FastIODebug : LIB_FastIO
    {
        Queue<string> param = new Queue<string>();
        string NextString() { if (param.Count == 0) foreach (var item in Console.ReadLine().Split(' ')) param.Enqueue(item); return param.Dequeue(); }
        public LIB_FastIODebug() { }
        public override string Scan() => NextString();
        public override long Long() => long.Parse(NextString());
        public override double Double() => double.Parse(NextString());
    }
    class LIB_Geo2D
    {
        static readonly public double EPS = 1e-10;
        public struct Vec
        {
            public double x;
            public double y;
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public Vec(double x, double y) { this.x = x; this.y = y; }
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            static public Vec operator +(Vec a, Vec b) => new Vec() { x = a.x + b.x, y = a.y + b.y };
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            static public Vec operator -(Vec a, Vec b) => new Vec() { x = a.x - b.x, y = a.y - b.y };
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            static public Vec operator *(Vec p, double v) => new Vec() { x = p.x * v, y = p.y * v };
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            static public Vec operator *(double v, Vec p) => p * v;
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            static public Vec operator /(Vec p, double v) => new Vec() { x = p.x / v, y = p.y / v };
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            static public Vec operator /(double v, Vec p) => p / v;
        }
        public struct Line
        {
            public double a;
            public double b;
            public double c;
            /// <summary>
            /// ax + by + c = 0
            /// </summary>
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public Line(double a, double b, double c) { this.a = a; this.b = b; this.c = c; }
        }
        public struct Circle
        {
            public Vec p;
            /// <summary>
            /// 半径の2乗
            /// </summary>
            public double r2;
            /// <summary>
            /// 半径
            /// </summary>
            public double r
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get { return Sqrt(r2); }
                private set { }
            }
        }
        /// <summary>
        /// 点と点の距離の2乗を求める
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public double Distance(Vec p1, Vec p2) => Norm(p2 - p1);
        /// <summary>
        /// 点と円の距離の2乗を求める。負の場合は円の内側にいる（絶対値は一番近い円の縁までの距離）
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public double Distance(Vec p, Circle c) => Norm(p - c.p) - c.r2;
        /// <summary>
        /// 点と円の距離の2乗を求める。負の場合は円の内側にいる（絶対値は一番近い円の縁までの距離）
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public double Distance(Circle c, Vec p) => Norm(p - c.p) - c.r2;
        /// <summary>
        /// 円と直線の交点を求める
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public Vec[] Intersection(Line l, Circle c) => Intersection(c, l);
        /// <summary>
        /// 円と直線の交点を求める
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public Vec[] Intersection(Circle c, Line l)
        {
            var d = l.a * c.p.x + l.b * c.p.y + l.c;
            var ab2 = (l.a * l.a + l.b * l.b);
            var d2 = ab2 * c.r2 - d * d;
            if (d2 < -EPS) return new Vec[0];
            if (d2 > EPS)
            {
                var rd = Sqrt(d2);
                var p1 = new Vec((-l.a * d + l.b * rd) / ab2 + c.p.x, (-l.b * d - l.a * rd) / ab2 + c.p.y);
                var p2 = new Vec((-l.a * d - l.b * rd) / ab2 + c.p.x, (-l.b * d + l.a * rd) / ab2 + c.p.y);
                return new[] { p1, p2 };
            }
            return new[] { new Vec(-l.a * d / ab2 + c.p.x, -l.b * d / ab2 + c.p.y) };
        }
        /// <summary>
        /// 円と円の交点を求める
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public Vec[] Intersection(Circle c1, Circle c2)
        {
            var p = c2.p - c1.p;
            var b = p.x * p.x + p.y * p.y;
            var a = (b + c1.r2 - c2.r2) / 2;
            var d = b * c1.r2 - a * a;
            if (d < -EPS) return new Vec[0];
            if (d > EPS)
            {
                var c = Sqrt(d);
                var p1 = new Vec((a * p.x + p.y * c) / b + c1.p.x, (a * p.y - p.x * c) / b + c1.p.y);
                var p2 = new Vec((a * p.x - p.y * c) / b + c1.p.x, (a * p.y + p.x * c) / b + c1.p.y);
                return new[] { p1, p2 };
            }
            return new[] { new Vec(a * p.x / b + c1.p.x, a * p.y / b + c1.p.y) };
        }
        /// <summary>
        /// pの長さの2乗を得る
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public double Norm(Vec p) => p.x * p.x + p.y * p.y;
        /// <summary>
        /// 内積
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public double Dot(Vec p1, Vec p2) => p1.x * p2.x + p1.y * p2.y;
        /// <summary>
        /// 外積（平行四辺形の面積）負になり得る
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public double Cross(Vec p1, Vec p2) => p1.x * p2.y - p1.y * p2.x;
        /// <summary>
        /// 3点を通る円を返す
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public Circle GetCircleFrom3Vec(Vec p1, Vec p2, Vec p3)
        {
            var A = Distance(p2, p3);
            var B = Distance(p1, p3);
            var C = Distance(p1, p2);
            var S = Abs(Cross(p2 - p1, p3 - p1));
            var p = (A * (B + C - A) * p1 + B * (C + A - B) * p2 + C * (A + B - C) * p3) / (4 * S * S);
            var r = Distance(p, p1);
            return new Circle() { p = p, r2 = r };
        }
        /// <summary>
        /// 2点を通る円を返す
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public Circle GetCircleFrom2Vec(Vec p1, Vec p2)
        {
            var c = (p1 + p2) / 2;
            return new Circle() { p = c, r2 = Distance(p1, c) };
        }
        /// <summary>
        /// 最小包含円を返す
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static public Circle GetEncloseCircle(IEnumerable<Vec> pointList)
        {
            var pList = pointList.ToArray();
            if (pList.Length < 2) throw new Exception();
            var rnd = new Random();
            var list = pList.OrderBy(_ => rnd.Next()).ToArray();
            Func<Vec, Circle, bool> inCircle = null;
            inCircle = (p, c) => Distance(p, c) < EPS;
            {
                var c = GetCircleFrom2Vec(list[0], list[1]);
                for (var i = 2; i < list.Length; i++)
                {
                    if (!inCircle(list[i], c))
                    {
                        c = GetCircleFrom2Vec(list[0], list[i]);
                        for (var j = 1; j < i; j++)
                        {
                            if (!inCircle(list[j], c))
                            {
                                c = GetCircleFrom2Vec(list[i], list[j]);
                                for (var k = 0; k < j; k++)
                                {
                                    if (!inCircle(list[k], c))
                                    {
                                        c = GetCircleFrom3Vec(list[i], list[j], list[k]);
                                    }
                                }
                            }
                        }
                    }
                }
                return c;
            }
        }
    }
}


Measured memory_bytes: 62260