using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			var cin = new Scanner2();
			double xs = cin.Double();
			double ys = cin.Double();
			double xt = cin.Double();
			double yt = cin.Double();
			int n = cin.Int();

			var xyr = new XYR[n + 2];
			xyr[0] = new XYR { X = xs, Y = ys, R = 0 };
			xyr[n + 1] = new XYR { X = xt, Y = yt, R = 0 };
			for (int i = 0; i < n; i++) {
				int x = cin.Int();
				int y = cin.Int();
				int r = cin.Int();
				xyr[i + 1] = new XYR { X = x, Y = y, R = r };
			}

			var d = new double[n + 2];
			for (int i = 0; i < n + 1; i++) {
				d[i + 1] = double.MaxValue;
			}

			var q = new PriorityQueue<PriorityPair<double, int>>(true);
			q.Enqueue(new PriorityPair<double, int>(0, 0));
			while (q.Count > 0) {
				var cur = q.Dequeue();

				if (d[cur.Item] < cur.Priority) {
					continue;
				}

				for (int i = 1; i <= n + 1; i++) {
					if (i == cur.Item) {
						continue;
					}

					double dd = Math.Max(
						0,
						Length(xyr[cur.Item], xyr[i])) + cur.Priority;
					if (d[i] > dd) {
						d[i] = dd;
						q.Enqueue(new PriorityPair<double, int>(dd, i));
					}
				}
			}

			double ans = d[n + 1];
			Console.WriteLine(ans);
		}

		public static double Length(XYR p1, XYR p2)
		{
			double l = Math.Sqrt(
				(p1.X - p2.X) * (p1.X - p2.X) + (p1.Y - p2.Y) * (p1.Y - p2.Y));
			return l - p1.R - p2.R;
		}

		public struct XYR
		{
			public double X { get; set; }
			public double Y { get; set; }
			public double R { get; set; }
		}
	}

	public class PriorityQueue<T>
	{
		private readonly List<T> heap_;
		private readonly Comparison<T> comparison_;
		private readonly bool reverses_;

		public T Top => heap_[0];
		public int Count => heap_.Count;

		public PriorityQueue(bool reverses = false)
			: this(Comparer<T>.Default, reverses) { }

		public PriorityQueue(int capacity, bool reverses = false)
			: this(capacity, Comparer<T>.Default.Compare, reverses) { }

		public PriorityQueue(IComparer<T> comparer, bool reverses = false)
			: this(16, comparer.Compare, reverses) { }

		public PriorityQueue(Comparison<T> comparison, bool reverses = false)
			: this(16, comparison, reverses) { }

		public PriorityQueue(
			int capacity,
			Comparison<T> comparison,
			bool reverses = false)
		{
			heap_ = new List<T>(capacity);
			comparison_ = comparison;
			reverses_ = reverses;
		}

		public void Enqueue(T item)
		{
			int c = heap_.Count;
			heap_.Add(item);
			while (c > 0) {
				int p = (c - 1) >> 1;
				if (Compare(p, c) < 0) {
					Swap(p, c);
				} else {
					break;
				}

				c = p;
			}
		}

		public T Dequeue()
		{
			T ret = heap_[0];
			int n = heap_.Count - 1;

			heap_[0] = heap_[n];
			heap_.RemoveAt(n);
			for (int p = 0, c; (c = (p << 1) + 1) < n; p = c) {
				if (c != n - 1 && Compare(c + 1, c) > 0) {
					++c;
				}

				if (Compare(p, c) < 0) {
					Swap(p, c);
				} else {
					break;
				}
			}

			return ret;
		}

		public void Clear() => heap_.Clear();

		private int Compare(int x, int y)
			=> comparison_(heap_[x], heap_[y]) * (reverses_ ? -1 : 1);

		private void Swap(int x, int y)
		{
			var t = heap_[x];
			heap_[x] = heap_[y];
			heap_[y] = t;
		}
	}

	public struct PriorityPair<T, U> : IComparable<PriorityPair<T, U>>
			where T : IComparable<T>
	{
		public T Priority { get; set; }
		public U Item { get; set; }

		public PriorityPair(T priority, U item)
		{
			Priority = priority;
			Item = item;
		}

		public int CompareTo(PriorityPair<T, U> target)
			=> Priority.CompareTo(target.Priority);

		public override string ToString()
			=> $"{Priority} {Item}";
	}

	public static class Helper
	{
		public static void UpdateMin32<T>(T array, int index, int value) where T : IList<int>
			=> array[index] = Math.Min(array[index], value);
		public static void UpdateMax32<T>(T array, int index, int value) where T : IList<int>
			=> array[index] = Math.Max(array[index], value);
		public static void UpdateMin64<T>(T array, int index, long value) where T : IList<long>
			=> array[index] = Math.Min(array[index], value);
		public static void UpdateMax64<T>(T array, int index, long value) where T : IList<long>
			=> array[index] = Math.Max(array[index], value);

		public static T[] Array<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToArray();
		public static List<T> List<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToList();
	}

	public class Scanner2
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private readonly Func<string> reader_;
		private string[] buf_;
		private int index_;

		public Scanner2(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		public int Int() => int.Parse(Next());
		public long Long() => long.Parse(Next());
		public double Double() => double.Parse(Next());

		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Int() + add;
			}
			return Array;
		}

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Long() + add;
			}
			return Array;
		}

		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Double() + add;
			}
			return Array;
		}

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}

Measured memory_bytes: 21216