import java.io.*;
import java.math.*;
import java.util.*;

import static java.util.Arrays.*;

public class Main {
	private static final int mod = (int)1e9+7;

	final Random random = new Random(0);
	final IOFast io = new IOFast();

	/// MAIN CODE
	public void run() throws IOException {
//		int TEST_CASE = Integer.parseInt(new String(io.nextLine()).trim());
		int TEST_CASE = 1;
		while(TEST_CASE-- != 0) {
			int xs = io.nextInt();
			int ys = io.nextInt();
			int xt = io.nextInt();
			int yt = io.nextInt();
			int n = io.nextInt();
			int[][] c = io.nextIntArray2D(n, 3);
			
			int S = n, T = n + 1;
			WeightedAdjListGraph g = new WeightedAdjListGraph(n + 2, (n + 2) * (n + 2));
			g.addEdge(S, T, dist(xt-xs, yt-ys, 0));
			for (int i = 0; i < n; i++) {
				g.addEdge(S, i, dist(c[i][0]-xs, c[i][1]-ys, c[i][2]));
				g.addEdge(i, T, dist(c[i][0]-xt, c[i][1]-yt, c[i][2]));
				for (int j = 0; j < i; j++) {
					g.addEdge(i, j, dist(c[i][0]-c[j][0], c[i][1]-c[j][1], c[i][2]+c[j][2]));
					g.addEdge(j, i, dist(c[i][0]-c[j][0], c[i][1]-c[j][1], c[i][2]+c[j][2]));
				}
			}
			
			io.out.printf("%.10f\n", g.dijkstra(S)[T]);
		}
	}
	
	static double dist(double dx, double dy, double sumC) {
		return Math.max(Math.sqrt(dx*dx+dy*dy)-sumC, 0.0);
	}
	
	static
	class WeightedAdjListGraph {
		int m, V, E;
		int[] head, next, to;
		double[] cost;
	
		public WeightedAdjListGraph(int V, int E) {
			head = new int[V];
			next = new int[E];
			cost = new double[E];
			to = new int[E];
			this.V = V;
			this.E = E;
			clear();
		}
	
		public void clear() {
			m = 0;
			Arrays.fill(head, -1);
		}
	
		public void addEdge(int s, int t, double c) {
//			if (c > eps) {
				next[m] = head[s];
				cost[m] = c;
				head[s] = m;
				to[m++] = t;
//			}
		}
		
		static class State implements Comparable<State> {
			final int v;
			final double c;
			
			public State(double c, int v) {
				this.v = v;
				this.c = c;
			}

			@Override
			public int compareTo(State o) {
				return Double.compare(c, o.c);
			}
		}
		
		static final double eps = 1e-9;
		public double[] dijkstra(final int s) {
			final double[] dist = new double[head.length];
			final PriorityQueue<State> q = new PriorityQueue<State>();

			Arrays.fill(dist, Double.POSITIVE_INFINITY);
			dist[s] = 0;
			q.add(new State(0, s));
			while(!q.isEmpty()) {
				final State xs = q.poll();
				final int v = xs.v;
				final double d = xs.c;
				if(dist[v] < d) continue;
				
				for(int e = head[v]; e != -1; e = next[e]) {
					final int t = to[e];
					final double w = d + cost[e];
//					dump(v, d, t, w);
					if(w + eps < dist[t]) {
						dist[t] = w;
						q.add(new State(w, t));
					}
				}
			}
			for(int i = 0; i < dist.length; i++) {
				if(dist[i] == Double.POSITIVE_INFINITY) {
					dist[i] = -1;
				}
			}
			return dist;
		}
		
	}
	

	/// TEMPLATE
	static int gcd(int n, int r) { return r == 0 ? n : gcd(r, n%r); }
	static long gcd(long n, long r) { return r == 0 ? n : gcd(r, n%r); }
	
	static <T> void swap(T[] x, int i, int j) { T t = x[i]; x[i] = x[j]; x[j] = t; }
	static void swap(int[] x, int i, int j) { int t = x[i]; x[i] = x[j]; x[j] = t; }

	void printArrayLn(int[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); }
	void printArrayLn(long[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); }
	
	static void dump(Object... o) { System.err.println(Arrays.deepToString(o)); } 
	
	void main() throws IOException {
		//		IOFast.setFileIO("rle-size.in", "rle-size.out");
		try { run(); }
		catch (EndOfFileRuntimeException e) { }
		io.out.flush();
	}
	public static void main(String[] args) throws IOException { new Main().main(); }
	
	static class EndOfFileRuntimeException extends RuntimeException {
		private static final long serialVersionUID = -8565341110209207657L; }

	static
	public class IOFast {
		private BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		private PrintWriter out = new PrintWriter(System.out);

		void setFileIn(String ins) throws IOException { in.close(); in = new BufferedReader(new FileReader(ins)); }
		void setFileOut(String outs) throws IOException { out.flush(); out.close(); out = new PrintWriter(new FileWriter(outs)); }
		void setFileIO(String ins, String outs) throws IOException { setFileIn(ins); setFileOut(outs); }

		private static int pos, readLen;
		private static final char[] buffer = new char[1024 * 8];
		private static char[] str = new char[500*8*2];
		private static boolean[] isDigit = new boolean[256];
		private static boolean[] isSpace = new boolean[256];
		private static boolean[] isLineSep = new boolean[256];

		static { for(int i = 0; i < 10; i++) { isDigit['0' + i] = true; } isDigit['-'] = true; isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true; isLineSep['\r'] = isLineSep['\n'] = true; }
		public int read() throws IOException { if(pos >= readLen) { pos = 0; readLen = in.read(buffer); if(readLen <= 0) { throw new EndOfFileRuntimeException(); } } return buffer[pos++]; }
		public int nextInt() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; int ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; }
		public long nextLong() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; long ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; }
		public char nextChar() throws IOException { while(true) { final int c = read(); if(!isSpace[c]) { return (char)c; } } }
		int reads(int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } if(str.length == len) { char[] rep = new char[str.length * 3 / 2]; System.arraycopy(str, 0, rep, 0, str.length); str = rep; } str[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; }
		int reads(char[] cs, int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } cs[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; }
		public char[] nextLine() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isLineSep); try { if(str[len-1] == '\r') { len--; read(); } } catch(EndOfFileRuntimeException e) { ; } return Arrays.copyOf(str, len); }
		public String nextString() throws IOException { return new String(next()); }
		public char[] next() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); return Arrays.copyOf(str, len); }
//		public int next(char[] cs) throws IOException { int len = 0; cs[len++] = nextChar(); len = reads(cs, len, isSpace); return len; }
		public double nextDouble() throws IOException { return Double.parseDouble(nextString()); }
		public long[] nextLongArray(final int n) throws IOException { final long[] res = new long[n]; for(int i = 0; i < n; i++) { res[i] = nextLong(); } return res; }
		public int[] nextIntArray(final int n) throws IOException { final int[] res = new int[n]; for(int i = 0; i < n; i++) { res[i] = nextInt(); } return res; }
		public int[][] nextIntArray2D(final int n, final int k) throws IOException { final int[][] res = new int[n][]; for(int i = 0; i < n; i++) { res[i] = nextIntArray(k); } return res; }
		public int[][] nextIntArray2DWithIndex(final int n, final int k) throws IOException { final int[][] res = new int[n][k+1]; for(int i = 0; i < n; i++) { for(int j = 0; j < k; j++) { res[i][j] = nextInt(); } res[i][k] = i; } return res; }
		public double[] nextDoubleArray(final int n) throws IOException { final double[] res = new double[n]; for(int i = 0; i < n; i++) { res[i] = nextDouble(); } return res; }
	}
}


Measured memory_bytes: 49840