#include <bits/stdc++.h>
#define REP(i, n) for(int i = 0; (i) < (n); (i)++)
using namespace std;

//Dijkstra
struct Edge{
    int to;
    double cost;
    Edge(int t, double c){
        to = t;
        cost = c;
    }
};
typedef pair<double, int> P;//距離、点

struct Dijkstra{
    int V;
    vector<vector<Edge>> G;
    vector<double> d;
    double inf = 1.0e18; // 10^18

    Dijkstra(int vv){
        V = vv;
        G.resize(V);
        d.resize(V);
    }

    void add_data(int a, int b, double c){
        Edge e1(b, c);
        G[a].push_back(e1);
    }

    void calc_dis(int s){
        priority_queue<P, vector<P>, greater<P>> que; //Pのfirstが小さい奴から取り出せる
        REP(i, V) d[i] = inf;
        d[s] = 0.0;
        que.push(P(0, s));

        while(!que.empty()){
            P p = que.top(); que.pop();
            int v = p.second;
            if(d[v] < p.first) continue;
            for(int i=0;i<G[v].size();i++){
                Edge e = G[v][i];
                if(d[e.to] > d[v] + e.cost){
                    d[e.to] = d[v] + e.cost;
                    que.push(P(d[e.to], e.to));
                }
            }
        }
    }
};

int main()
{   
    int N, M; cin >> N >> M;
    int X, Y; cin >> X >> Y;
    int p[200005], q[200005];
    REP(i, N) cin >> p[i] >> q[i];
    int P[200005], Q[200005];
    REP(i, M) cin >> P[i] >> Q[i];

    Dijkstra dk(N);
    REP(i, M){
        double dis = sqrt((double)((p[P[i]-1] - p[Q[i]-1]) * (p[P[i]-1] - p[Q[i]-1]) + (q[P[i]-1] - q[Q[i]-1]) * (q[P[i]-1] - q[Q[i]-1])));
        //cout << dis << endl;
        dk.add_data(P[i]-1, Q[i]-1, dis);
        dk.add_data(Q[i]-1, P[i]-1, dis);
    } 
    dk.calc_dis(X-1);
    //REP(i, N) cout << dk.d[i] << endl;
    cout << fixed;
    cout << setprecision(8) << dk.d[Y-1] << endl;

    return 0;
}