using static System.Math;
using System.Collections.Generic;
using System;

public class PriorityQueue<T> where T : IComparable
{
    private IComparer<T> _comparer = null;
    private int _type = 0;
    private T[] _heap;
    private int _sz = 0;
    private int _count = 0;
    public PriorityQueue(int maxSize, IComparer<T> comparer)
    {
        _heap = new T[maxSize];
        _comparer = comparer;
    }
    public PriorityQueue(int maxSize, int type = 0)
    {
        _heap = new T[maxSize];
        _type = type;
    }
    private int Compare(T x, T y)
    {
        if (_comparer != null) return _comparer.Compare(x, y);
        return _type == 0 ? x.CompareTo(y) : y.CompareTo(x);
    }
    public void Push(T x)
    {
        _count++;
        var i = _sz++;
        while (i > 0)
        {
            var p = (i - 1) / 2;

            if (Compare(_heap[p], x) <= 0) break;

            _heap[i] = _heap[p];
            i = p;
        }
        _heap[i] = x;
    }
    public T Pop()
    {
        _count--;
        T ret = _heap[0];
        T x = _heap[--_sz];

        int i = 0;
        while (i * 2 + 1 < _sz)
        {
            int a = i * 2 + 1;
            int b = i * 2 + 2;

            if (b < _sz && Compare(_heap[b], _heap[a]) < 0) a = b;

            if (Compare(_heap[a], x) >= 0) break;

            _heap[i] = _heap[a];
            i = a;
        }
        _heap[i] = x;
        return ret;
    }
    public int Count()
    {
        return _count;
    }
    public T Peek()
    {
        return _heap[0];
    }
    public bool Contains(T x)
    {
        for (int i = 0; i < _sz; i++) if (x.Equals(_heap[i])) return true;
        return false;
    }
    public void Clear()
    {
        while (this.Count() > 0) this.Pop();
    }
    public IEnumerator<T> GetEnumerator()
    {
        var ret = new List<T>();
        while (this.Count() > 0)
        {
            ret.Add(this.Pop());
        }
        foreach (var r in ret)
        {
            this.Push(r);
            yield return r;
        }
    }
    public T[] ToArray()
    {
        T[] array = new T[_sz];
        int i = 0;
        foreach (var r in this)
        {
            array[i++] = r;
        }
        return array;
    }
}
public class Edge
{
    public int to { get; set; }
    public double d { get; set; }
}
public class Node : IComparable
{
    public int id { get; set; }
    public double d { get; set; }
    public int CompareTo(object obj)
    {
        var x = (Node)obj;
        if (this.d > x.d) return 1;
        else if (this.d == x.d) return 0;
        else return -1;
    }
}

public class P
{
    public int x { get; set; }
    public int y { get; set; }
}

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var m = int.Parse(line[1]);
        line = Console.ReadLine().Trim().Split(' ');
        var r = int.Parse(line[0]) - 1;
        var r2 = int.Parse(line[1]) - 1;
        var ps = new P[n];
        var aa = new List<Edge>[n];
        for (int i = 0; i < n; i++)
        {
            line = Console.ReadLine().Trim().Split(' ');
            ps[i] = new P { x = int.Parse(line[0]), y = int.Parse(line[1]) };
            aa[i] = new List<Edge>();
        }
        for (int i = 0; i < m; i++)
        {
            line = Console.ReadLine().Trim().Split(' ');
            var p = int.Parse(line[0]) - 1;
            var q = int.Parse(line[1]) - 1;
            var wd = Sqrt((ps[p].x - ps[q].x) * (ps[p].x - ps[q].x) + (ps[p].y - ps[q].y) *
                (ps[p].y - ps[q].y));
            aa[p].Add(new Edge { to = q, d = wd });
            aa[q].Add(new Edge { to = p, d = wd });
        }
        var mind = new double[n];
        for (int i = 0; i < n; i++) mind[i] = 100000000000d;
        goDijk(aa, r, n, mind);
        Console.WriteLine(mind[r2]);
    }
    public static void goDijk(List<Edge>[] aa, int r, int n, double[] mind)
    {
        var pq = new PriorityQueue<Node>(n + 1000, 0);
        pq.Push(new Node { id = r, d = 0 });
        while (pq.Count() > 0)
        {
            var targ = pq.Pop();
            var nowd = targ.d;
            var nowid = targ.id;
            if (mind[nowid] < nowd) continue;
            mind[nowid] = nowd;
            foreach (var x in aa[nowid])
                if (nowd + x.d < mind[x.to])
                {
                    mind[x.to] = nowd + x.d;
                    pq.Push(new Node { id = x.to, d = nowd + x.d });
                }

        }
    }
}