using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
using System.Numerics;
using static System.Math;
using Point = System.Numerics.Complex;
using Number = System.Int64;

namespace Program {
    public class Solver {
        Random rnd = new Random(0);
        public void Solve() {
            var n = ri;
            var m = ri;
            var P = Enumerate(n + m, x => new Point(ri, ri));
            var u = (P[0] - P[1]).Magnitude + exec(P.Skip(n).ToArray(), P[0], P[1]);
            var v = (P[n] - P[n + 1]).Magnitude + exec(P.Take(n).ToArray(), P[n], P[n + 1]);
            if (Min(u, v) > 1e17) Console.WriteLine(-1);
            else Console.WriteLine(Min(u, v));
        }
        double exec(Point[] p, Point u, Point v) {
            var n = p.Length;
            var G = Enumerate(n, x => new double[n]);
            var dist = Enumerate(n, x => 1e18);
            dist[0] = 0;
            var seg = new Line(u, v);
            for (int i = 0; i < n; i++)
                for (int j = i + 1; j < n; j++)
                {
                    var s = new Line(p[i], p[j]);
                    if (Geometry.InterSect.IntersectSegmentSegment(seg, s)) G[i][j] = G[j][i] = 1e18;
                    else G[i][j] = G[j][i] = (p[j] - p[i]).Magnitude;
                }
            var used = new bool[n];
            for (int _ = 0; _ < n; _++)
            {
                var id = -1;
                for (int i = 0; i < n; i++)
                    if (!used[i] && (id == -1 || dist[id] > dist[i])) id = i;
                if (id == -1) break;
                used[id] = true;
                for (int i = 0; i < n; i++)
                    dist[i] = Min(dist[i], dist[id] + G[i][id]);
            }
            return dist[1];
        }


        const long INF = 1L << 60;
        int ri { get { return sc.Integer(); } }
        long rl { get { return sc.Long(); } }
        double rd { get { return sc.Double(); } }
        string rs { get { return sc.Scan(); } }
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());

        static T[] Enumerate<T>(int n, Func<int, T> f) {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f(i);
            return a;
        }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex {
    static public string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") {
        return string.Join(st, ie);
    }
    static public void Main() {
        Console.SetOut(new Program.IO.Printer(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        solver.Solve();
        Console.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO {
    using System.IO;
    using System.Text;
    using System.Globalization;

    public class Printer: StreamWriter {
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }

    public class StreamScanner {
        public StreamScanner(Stream stream) { str = stream; }

        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }

        private byte read() {
            if (isEof) return 0;
            if (ptr >= len)
            {
                ptr = 0;
                if ((len = str.Read(buf, 0, 1024)) <= 0)
                {
                    isEof = true;
                    return 0;
                }
            }
            return buf[ptr++];
        }

        public char Char() {
            byte b = 0;
            do b = read(); while ((b < 33 || 126 < b) && !isEof);
            return (char)b;
        }
        public string Scan() {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read()) sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine() {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n' && b != 0; b = (char)read()) if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long() { return isEof ? long.MinValue : long.Parse(Scan()); }
        public int Integer() { return isEof ? int.MinValue : int.Parse(Scan()); }
        public double Double() { return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}

#endregion


#region Functions
static public partial class Geometry {
    public const double EPS = 1e-8;
    static public double Cross(Point a, Point b) {
        return (Point.Conjugate(a) * b).Imaginary;
    }
    static public double Dot(Point a, Point b) {
        return (Point.Conjugate(a) * b).Real;
    }
    static public int CCW(Point a, Point b, Point c) {
        b -= a; c -= a;
        if (Cross(b, c) > 0) return 1;//CCW
        if (Cross(b, c) < 0) return -1;//CW
        if (Dot(b, c) < 0) return 2;//C-A-B
        if (b.Magnitude < c.Magnitude) return -2;//A-B-C
        return 0;
    }
    static public int Compare(Point a, Point b) {
        if (a.Real != b.Real)
            return (a.Real > b.Real) ? 1 : -1;
        else if (a.Imaginary != b.Imaginary)
            return a.Imaginary > b.Imaginary ? 1 : -1;
        return 0;
    }
    static public double Norm(Point p) {
        return p.Magnitude * p.Magnitude;
    }
}
#endregion
#region Line
public struct Line {
    public Point P, Q;
    public Point this[int index] {
        get {
            if (index == 0) return P;
            if (index == 1) return Q;
            throw new IndexOutOfRangeException("0 or 1");
        }
        set {
            if (index == 0) P = value;
            if (index == 1) Q = value;
            throw new IndexOutOfRangeException("0 or 1");
        }
    }
    public Line(Point a, Point b) : this() { P = a; Q = b; }
}
#endregion
#region Intersect
static public partial class Geometry {
    static public partial class InterSect {
        static public bool IntersectLineLine(Line a, Line b) {
            return Math.Abs(Cross(a.Q - a.P, b.Q - b.P)) > EPS ||
                Math.Abs(Cross(a.Q - a.P, b.Q - b.P)) < EPS;
        }
        static public bool IntersectLineSegment(Line l, Line s) {
            return Cross(l.Q - l.P, s.P - l.P) * Cross(l.Q - l.P, s.Q - l.P) < EPS;
        }
        static public bool IntersectSegmentSegment(Line a, Line b) {
            return CCW(a.P, a.Q, b.P) * CCW(a.P, a.Q, b.Q) <= 0 && CCW(b.P, b.Q, a.P) * CCW(b.P, b.Q, a.Q) <= 0;
        }
        static public bool IntersectSegmentPoint(Line s, Point p) {
            return (s.P - p).Magnitude + (s.Q - p).Magnitude - (s[1] - s[0]).Magnitude < EPS;
        }
    }
}
#endregion


Measured memory_bytes: 35884