Every true king during his life must conquer the world, hold the Codeforces world finals, win pink panda in the shooting gallery and travel all over his kingdom.

King Copa has already done the first three things. Now he just needs to travel all over the kingdom. The kingdom is an infinite plane with Cartesian coordinate system on it. Every city is a point on this plane. There are n cities in the kingdom at points with coordinates (x1, 0), (x2, 0), ..., (xn, 0), and there is one city at point (xn + 1, yn + 1). 

King starts his journey in the city number k. Your task is to find such route for the king, which visits all cities (in any order) and has minimum possible length. It is allowed to visit a city twice. The king can end his journey in any city. Between any pair of cities there is a direct road with length equal to the distance between the corresponding points. No two cities may be located at the same point.

Input

The first line contains two integers n and k (1 ≤ n ≤ 105, 1 ≤ k ≤ n + 1) — amount of cities and index of the starting city. The second line contains n + 1 numbers xi. The third line contains yn + 1. All coordinates are integers and do not exceed 106 by absolute value. No two cities coincide.

Output

Output the minimum possible length of the journey. Your answer must have relative or absolute error less than 10 - 6.

Examples

Input

3 1
0 1 2 1
1


Output

3.41421356237309490000

Input

3 1
1 0 2 1
1


Output

3.82842712474619030000

Input

4 5
0 5 -1 -5 2
3


Output

14.24264068711928400000
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Comparator;
import java.util.InputMismatchException;

/**
 * @author Egor Kulikov (egor@egork.net)
 *         Created on 14.03.2010
 */
public class TaskD implements Runnable {
	private InputReader in;
	private PrintWriter out;

	public static void main(String[] args) {
//		new Thread(new Template()).start();
		new TaskD().run();
	}

	public TaskD() {
//		String id = getClass().getName().toLowerCase();
//		try {
//			System.setIn(new FileInputStream(id + ".in"));
//			System.setOut(new PrintStream(new FileOutputStream(id + ".out")));
//			System.setIn(new FileInputStream("input.txt"));
//			System.setOut(new PrintStream(new FileOutputStream("output.txt")));
//		} catch (FileNotFoundException e) {
//			throw new RuntimeException();
//		}
		in = new InputReader(System.in);
		out = new PrintWriter(System.out);
	}

	public void run() {
//        int numTests = in.readInt();
//        for (int testNumber = 0; testNumber < numTests; testNumber++) {
		process();
//        }
		out.close();
	}

	private void process() {
		int n = in.readInt();
		int k = in.readInt();
		final int[] x = new int[n + 1];
		for (int i = 0; i <= n; i++)
			x[i] = in.readInt();
		int y = in.readInt();
		double ans;
		int minIndex = 0;
		int maxIndex = 0;
		int min = x[0];
		int max = x[0];
		for (int i = 1; i < n; i++) {
			if (x[i] < min) {
				min = x[i];
				minIndex = i;
			}
			if (x[i] > max) {
				max = x[i];
				maxIndex = i;
			}
		}
		Integer[] o = new Integer[n];
		for (int i = 0; i < n; i++)
			o[i] = i;
		Arrays.sort(o, new Comparator<Integer>() {
			public int compare(Integer o1, Integer o2) {
				return x[o1] - x[o2];
			}
		});
		int[] oo = new int[n];
		for (int i = 0; i < n; i++)
			oo[o[i]] = i;
		if (k == n + 1)
			ans = x[maxIndex] - x[minIndex] + Math.min(Math.hypot(x[n] - x[minIndex], y), Math.hypot(x[n] - x[maxIndex], y));
		else {
			int start = oo[k - 1];
			Arrays.sort(x, 0, n);
			ans = Math.hypot(x[start] - x[n], y) + Math.hypot(x[0] - x[n], y) + x[n - 1] - x[0];
			ans = Math.min(ans, Math.hypot(x[start] - x[n], y) + Math.hypot(x[n - 1] - x[n], y) + x[n - 1] - x[0]);
			ans = Math.min(ans, x[start] - x[0] + x[n - 1] - x[0] + Math.hypot(x[n - 1] - x[n], y));
			ans = Math.min(ans, x[n - 1] - x[start] + x[n - 1] - x[0] + Math.hypot(x[0] - x[n], y));
			for (int i = 1; i < n; i++) {
				if (start >= i) {
					double v1 = Math.min(x[start] - x[i] + x[n - 1] - x[i] + Math.hypot(x[n - 1] - x[n], y), x[n - 1] - x[start] + x[n - 1] - x[i] + Math.hypot(x[n] - x[i], y));
					double v2 = x[i - 1] - x[0] + Math.min(Math.hypot(x[i - 1] - x[n], y), Math.hypot(x[0] - x[n], y));
					ans = Math.min(ans, v1 + v2);
				} else {
					double v1 = Math.min(x[start] - x[0] + x[i - 1] - x[0] + Math.hypot(x[i - 1] - x[n], y), x[i - 1] - x[start] + x[i - 1] - x[0] + Math.hypot(x[n] - x[0], y));
					double v2 = x[n - 1] - x[i] + Math.min(Math.hypot(x[n - 1] - x[n], y), Math.hypot(x[i] - x[n], y));
					ans = Math.min(ans, v1 + v2);
				}
			}
		}
		out.printf("%.8f\n", ans);
	}

	private static class InputReader {
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar, numChars;

		public InputReader(InputStream stream) {
			this.stream = stream;
		}

		private int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		public int readInt() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}

		public long readLong() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}

		public String readString() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuffer res = new StringBuffer();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}

		private boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		private String readLine0() {
			StringBuffer buf = new StringBuffer();
			int c = read();
			while (c != '\n' && c != -1) {
				buf.appendCodePoint(c);
				c = read();
			}
			return buf.toString();
		}

		public String readLine() {
			String s = readLine0();
			while (s.trim().length() == 0)
				s = readLine0();
			return s;
		}

		public String readLine(boolean ignoreEmptyLines) {
			if (ignoreEmptyLines)
				return readLine();
			else
				return readLine0();
		}

		public BigInteger readBigInteger() {
			try {
				return new BigInteger(readString());
			} catch (NumberFormatException e) {
				throw new InputMismatchException();
			}
		}

		public char readCharacter() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			return (char) c;
		}

		public double readDouble() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			double res = 0;
			while (!isSpaceChar(c) && c != '.') {
				if (c < '0' || c > '9') {
					if (c == 'e' || c == 'E') {
						int e = readInt();
						return res * Math.pow(10, e);
					}
					throw new InputMismatchException();
				}
				res *= 10;
				res += c - '0';
				c = read();
			}
			if (c == '.') {
				c = read();
				double m = 1;
				while (!isSpaceChar(c)) {
					if (c == 'e' || c == 'E') {
						int e = readInt();
						return res * Math.pow(10, e);
					}
					if (c < '0' || c > '9')
						throw new InputMismatchException();
					m /= 10;
					res += (c - '0') * m;
					c = read();
				}
			}
			return res * sgn;
		}
	}
}