Problem: The Kingdom of Neva is home to two ethnic groups, the Totata and the Tutete. The biggest feature of the Totata tribe is that they eat sweet and sour pork with pineapple. However, the Tutete tribe eats vinegared pork in pineapple. These two peoples couldn't get along with each other, and the Totata and Tutete have been in conflict for hundreds of years.

One day, a petition arrived from two ethnic groups under King Neva. According to it, the Totata tribe wants to build a road connecting the town A and the town B where they live. On the other hand, the Tutete tribe also wants to build a road connecting the town C and the town D where they live.

To prevent the two races from clashing, the roads of the Totata and Tutete cannot be crossed. Also, due to technical restrictions, it is only possible to build a road that connects the two cities in a straight line. In other words, if necessary, instead of connecting city A and city B directly with a road, it would indirectly connect city A and city B via some Totata towns (of course, of the Tutete tribe). Do not go through the city). At that time, the roads connecting the towns of the Totata tribe may intersect. The same applies to town C and town D.

Building a road costs proportional to its length. Therefore, I would like to make the total length of the roads to be constructed as short as possible while satisfying the conditions. Now, what is the minimum length?



Input

NA NB
xA, 1 yA, 1
xA, 2 yA, 2
..
..
..
xA, NA yA, NA
xB, 1 yB, 1
xB, 2 yB, 2
..
..
..
xB, NB yB, NB


The integer NA (2 ≤ NA ≤ 1,000) and the integer NB (2 ≤ NB ≤ 1,000) are written on the first line of the input, separated by blanks. This means that there are NA towns where the Totata tribe lives and NB towns where the Tutete tribe lives in the Kingdom of Neva. In the initial state, no road has been built anywhere.

The following NA line contains the integers xA, i (-10,000 ≤ xA, i ≤ 10,000) and the integers yA, i (-10,000 ≤ yA, i ≤ 10,000), separated by blanks. The geography of the Kingdom of Neva is represented by a two-dimensional Cartesian coordinate plane, and the integers xA, i and yA, i written on the 1 + i line are the position coordinates of the i-th city where the Totata tribe lives (xA, i, yA). , I). (xA, 1, yA, 1) and (xA, 2, yA, 2) are the coordinates of the two cities to be connected.

On the following NB line, the integers xB, i (-10,000 ≤ xB, i ≤ 10,000) and the integers yB, i (-10,000 ≤ yB, i ≤ 10,000) are written separated by blanks. The integers xB, i and yB, i written on the 1 + NA + i line indicate that the position coordinates of the i-th city where the Ytterbium live are (xB, i, yB, i). (xB, 1, yB, 1) and (xB, 2, yB, 2) are the coordinates of the two cities to be connected.

It can be assumed that the coordinates of the two cities are different and that none of the three cities are on the same straight line.

Output

When the road is constructed so as to meet the conditions of the problem statement, output the minimum value of the total length of the road. The "length" here is the Euclidean distance. However, if you cannot build a road that meets the conditions, output -1 instead. The output may contain errors, but the relative error to the true value must be less than 10-9.

Examples

Input

2 2
0 0
1 1
2 0
2 -1


Output

2.414213562373


Input

2 3
4 0
0 0
2 3
2 -2
3 1


Output

-1


Input

5 2
-2 1
1 2
-1 3
-1 5
1 4
0 4
0 0


Output

12.359173603117

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.HashMap;
import java.util.PriorityQueue;
import java.util.Queue;

public class Main {
	static ContestScanner in;
	static Writer out;
	public static void main(String[] args) {
		Main main = new Main();
		try {
			in = new ContestScanner();
			out = new Writer();
			main.solve();
			out.close();
			in.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	void solve() throws IOException {
		int na = in.nextInt();
		int nb = in.nextInt();
		Pos[] a = new Pos[na];
		Pos[] b = new Pos[nb];
		for(int i = 0; i < na; i++) {
			a[i] = new Pos(in.nextInt(), in.nextInt());
		}
		for(int i = 0; i < nb; i++) {
			b[i] = new Pos(in.nextInt(), in.nextInt());
		}
		double ans = shortest(a, b[0], b[1]);
		ans = Math.min(ans, shortest(b, a[0], a[1]));
		if(ans >= inf) out.println(-1);
		else out.println(ans);
	}
	
	final double inf = 1e9;
	double shortest(Pos[] p, Pos s1, Pos s2) {
		int n = p.length;
		double[] d = new double[n];
		Arrays.fill(d, inf);
		Queue<St> qu = new PriorityQueue<>();
		qu.add(new St(0, 0));
		while(!qu.isEmpty()) {
			St s = qu.poll();
			if(d[s.p] < inf) continue;
			d[s.p] = s.d;
			if(s.p == 1) {
				return s1.dist(s2) + s.d;
			}
			for(int i = 0; i < n; i++) {
				if(d[i] < inf) continue;
				if(cross(s1, s2, p[s.p], p[i])) continue;
				qu.add(new St(i, s.d + p[s.p].dist(p[i])));
			}
		}
		return inf;
	}
	
	static boolean cross(Pos p1, Pos p2, Pos p3, Pos p4){
		return ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 && ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0;
	}
	static double cross(Pos a, Pos b){
		return a.x*b.y - b.x*a.y;
	}
	public static double cross(double x1, double y1, double x2, double y2){
		return x1*y2 - x2*y1;
	}
	// ?????£??§?¨???§???????¨????????????£
	// ?????£???????????¶????????????
	static double ccw(Pos a, Pos b, Pos c){
		double dx1 = b.x - a.x;
		double dy1 = b.y - a.y;
		double dx2 = c.x - a.x;
		double dy2 = c.y - a.y;
		return dx1*dy2 - dx2*dy1;
	}
}

class St implements Comparable<St>{
	double d;
	int p;
	public St(int p, double d) {
		this.p = p;
		this.d = d;
	}
	@Override
	public int compareTo(St o) {
		return Double.compare(d, o.d);
	}
}

class Pos {
	int x, y;
	public Pos(int x, int y) {
		this.x = x;
		this.y = y;
	}
	
	double dist(Pos p) {
		return Math.sqrt(sq(x - p.x) + sq(y - p.y));
	}
	
	long sq(long a) {
		return a * a;
	}
}

@SuppressWarnings("serial")
class MultiSet<T> extends HashMap<T, Integer>{
	@Override public Integer get(Object key){return containsKey(key)?super.get(key):0;}
	public void add(T key,int v){put(key,get(key)+v);}
	public void add(T key){put(key,get(key)+1);}
	public void sub(T key){final int v=get(key);if(v==1)remove(key);else put(key,v-1);}
	public MultiSet<T> merge(MultiSet<T> set)
	{MultiSet<T>s,l;if(this.size()<set.size()){s=this;l=set;}else{s=set;l=this;}
	for(Entry<T,Integer>e:s.entrySet())l.add(e.getKey(),e.getValue());return l;}
}

class Writer extends PrintWriter{
	public Writer(String filename)throws IOException
	{super(new BufferedWriter(new FileWriter(filename)));}
	public Writer()throws IOException{super(System.out);}
}
class ContestScanner implements Closeable{
	private BufferedReader in;private int c=-2;
	public ContestScanner()throws IOException 
	{in=new BufferedReader(new InputStreamReader(System.in));}
	public ContestScanner(String filename)throws IOException
	{in=new BufferedReader(new InputStreamReader(new FileInputStream(filename)));}
	public String nextToken()throws IOException {
		StringBuilder sb=new StringBuilder();
		while((c=in.read())!=-1&&Character.isWhitespace(c));
		while(c!=-1&&!Character.isWhitespace(c)){sb.append((char)c);c=in.read();}
		return sb.toString();
	}
	public String readLine()throws IOException{
		StringBuilder sb=new StringBuilder();if(c==-2)c=in.read();
		while(c!=-1&&c!='\n'&&c!='\r'){sb.append((char)c);c=in.read();}
		return sb.toString();
	}
	public long nextLong()throws IOException,NumberFormatException
	{return Long.parseLong(nextToken());}
	public int nextInt()throws NumberFormatException,IOException
	{return(int)nextLong();}
	public double nextDouble()throws NumberFormatException,IOException 
	{return Double.parseDouble(nextToken());}
	public void close() throws IOException {in.close();}
}