import static java.lang.Math.*;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.PriorityQueue;
import java.util.stream.Stream;

public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		MyInput in = new MyInput(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskX solver = new TaskX();
		solver.solve(1, in, out);
		out.close();
	}

	static int INF = 1 << 30;
	static long LINF = 1L << 55;
	static int MOD = 1000000007;
	static int[] mh4 = { 0, -1, 1, 0 };
	static int[] mw4 = { -1, 0, 0, 1 };
	static int[] mh8 = { -1, -1, -1, 0, 0, 1, 1, 1 };
	static int[] mw8 = { -1, 0, 1, -1, 1, -1, 0, 1 };

	static class TaskX {

		@SuppressWarnings("unchecked")
		public void solve(int testNumber, MyInput in, PrintWriter out) {

			T s = new T(1001, in.nextLong(), in.nextLong(), 0);
			T t = new T(1002, in.nextLong(), in.nextLong(), 0);
			int n = in.nextInt();
			T[] ts = new T[1010];
			for (int i = 0; i < n; i++) {
				ts[i] = new T(i, in.nextLong(), in.nextLong(), in.nextLong());
			}

			List<P>[] g = new ArrayList[1010];
			g = Stream.generate(ArrayList::new).limit(1010).toArray(List[]::new);

			for (int i = 0; i < n; i++) {
				g[1001].add(new P(ts[i].idx, dist(s, ts[i])));
				g[ts[i].idx].add(new P(1001, dist(s, ts[i])));
			}

			for (int i = 0; i < n; i++) {
				g[1002].add(new P(ts[i].idx, dist(t, ts[i])));
				g[ts[i].idx].add(new P(1002, dist(t, ts[i])));
			}

			g[s.idx].add(new P(t.idx, dist(s, t)));
			g[t.idx].add(new P(s.idx, dist(s, t)));

			for (int from = 0; from < n; from++) {
				for (int to = 0; to < n; to++) {
					if (from == to) continue;
					g[ts[from].idx].add(new P(ts[to].idx, dist(ts[from], ts[to])));
				}
			}

			double[] cost = new double[1010];
			Arrays.fill(cost, Double.MAX_VALUE/2);
			cost[1001] = 0.0;

			PriorityQueue<P> pq = new PriorityQueue<>();
			pq.add(new P(1001, cost[1001]));
			while (!pq.isEmpty()) {
				P now = pq.remove();

				if (now.d != cost[now.idx]) continue;

				for (P to : g[now.idx]) {
					if (cost[now.idx] + to.d < cost[to.idx]) {
						cost[to.idx] = cost[now.idx] + to.d;
						pq.add(new P(to.idx, cost[to.idx]));
					}
				}
			}

			out.println(cost[1002]);

		}

		class P implements Comparable<P> {
			int idx;
			double d;

			public P(int idx, double d) {
				super();
				this.idx = idx;
				this.d = d;
			}

			@Override
			public int compareTo(P o) {
				return Double.compare(this.d, o.d);
			}

			@Override
			public String toString() {
				return "P [idx=" + idx + ", d=" + d + "]";
			}

		}

		double dist (T t1, T t2) {
			double ret = sqrt(pow(t1.x - t2.x, 2) + pow(t1.y - t2.y, 2));
			ret -= t1.r + t2.r;
			return Math.max(ret, 0);
		}

		class T {
			int idx;
			long x, y, r;

			public T(int idx, long x, long y, long r) {
				super();
				this.idx = idx;
				this.x = x;
				this.y = y;
				this.r = r;
			}

			@Override
			public String toString() {
				return "T [idx=" + idx + ", x=" + x + ", y=" + y + ", r=" + r
						+ "]";
			}

		}
	}

	static class MyInput {
		private final BufferedReader in;
		private static int pos;
		private static int 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 MyInput(InputStream is) {
			in = new BufferedReader(new InputStreamReader(is));
		}

		public int read() {
			if (pos >= readLen) {
				pos = 0;
				try {
					readLen = in.read(buffer);
				} catch (IOException e) {
					throw new RuntimeException();
				}
				if (readLen <= 0) {
					throw new MyInput.EndOfFileRuntimeException();
				}
			}
			return buffer[pos++];
		}

		public int nextInt() {
			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() {
			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() {
			while (true) {
				final int c = read();
				if (!isSpace[c]) {
					return (char) c;
				}
			}
		}

		public String nextString() {
			return new String(nextChars());
		}

		public char[] nextChars() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			return Arrays.copyOf(str, len);
		}

		public char[][] next2DChars(int h, int w) {
			char[][] s = new char[h][w];
			for (int i = 0; i < h; i++) {
				s[i] = nextChars();
			}
			return s;
		}

		int reads(int len, boolean[] accept) {
			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 (MyInput.EndOfFileRuntimeException e) {
			}
			return len;
		}

		public int[] nextIntArray(final int n) {
			final int[] res = new int[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextInt();
			}
			return res;
		}

		public int[] nextIntArray1Index(final int n) {
			final int[] res = new int[n + 1];
			for (int i = 1; i < n + 1; i++) {
				res[i] = nextInt();
			}
			return res;
		}

		public int[] nextIntArrayDec(final int n) {
			final int[] res = new int[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextInt() - 1;
			}
			return res;
		}

		public long[] nextLongArray(final int n) {
			final long[] res = new long[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextLong();
			}
			return res;
		}

		public long[] nextLongArray1Index(final int n) {
			final long[] res = new long[n + 1];
			for (int i = 1; i < n + 1; i++) {
				res[i] = nextLong();
			}
			return res;
		}

		public long[] nextLongArrayDec(final int n) {
			final long[] res = new long[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextLong() - 1;
			}
			return res;
		}

		public double nextDouble() {
			return Double.parseDouble(nextString());
		}

		public double[] nextDoubleArray(int n) {
			double[] res = new double[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextDouble();
			}
			return res;
		}

		static class EndOfFileRuntimeException extends RuntimeException {
		}

	}

}


Measured memory_bytes: 113256