#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cmath>

using namespace std;
typedef long long ll;

const double INF = 1e+15;

typedef pair<double, int> P;

struct edge{
    int to;
    double cost;
};

double d[200000];

void dijkstra(int s, int num_v, vector<edge> G[]){
    priority_queue<P, vector<P>, greater<P>> que;
    fill(d, d+num_v, INF);
    d[s] = 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[v] + e.cost < d[e.to]){
                d[e.to] = d[v] + e.cost;
                que.push(P(d[e.to], e.to));
            }
        }
    }
}

double dist(double xa, double xb, double ya, double yb){
    return sqrt((xa-xb)*(xa-xb)+(ya-yb)*(ya-yb));
}

vector<edge> G[200000];
int N, M, X, Y;
double p[200000], q[200000];

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    cin >> N >> M >> X >> Y;
    X--; Y--;
    for(int i = 0; i < N; i++) cin >> p[i] >> q[i];
    for(int i = 0; i < M; i++){
        int P, Q;
        cin >> P >> Q;
        P--; Q--;
        G[P].push_back((edge){Q, dist(p[P], p[Q], q[P], q[Q])});
        G[Q].push_back((edge){P, dist(p[P], p[Q], q[P], q[Q])});
    }
    dijkstra(X, N, G);
    cout << d[Y] << endl;
}