#include <bits/stdc++.h>
using namespace std;
double calc_dist(int x1, int y1, int x2, int y2){
    long long tmpx = (x1 - x2) * (x1 - x2);
    long long tmpy = (y1 - y2) * (y1 - y2);
    return sqrt(tmpx + tmpy);
}
int main(void){
    // Your code here!
    int N, M;
    cin >> N >> M;
    int X, Y;
    cin >> X >> Y;
    X--;
    Y--;
    map<int, vector<int>> D;
    vector<pair<int, int>> p(N);
    int x, y;
    for (int i=0;i<N;i++){
        cin >> x >> y;
        p[i] = make_pair(x, y);
    }
    for (int i=0;i<M;i++){
        cin >> x >> y;
        x--;
        y--;
        if (D.count(x)){
            D[x].push_back(y);
        }
        else{
            D[x] = {y};
        }
        if (D.count(y)){
            D[y].push_back(x);
        }
        else{
            D[y] = {x};
        }
    }
    priority_queue<pair<double, int>, vector<pair<double, int>>, greater<pair<double, int>>> pq;
    vector<double> dist(N, 1e9);
    dist[X] = 0.0;
    for (int i=0;i<N;i++){
        pq.push(make_pair(dist[i], i));
    }
    pair<double, int> tmp;
    int r;
    while (!pq.empty()){
        tmp = pq.top();
        pq.pop();
        r = tmp.second;
        if (D.count(r)){
            for (int i: D[r]){
                if (dist[i] > dist[r] + calc_dist(p[i].first, p[i].second, p[r].first, p[r].second)){
                    dist[i] = dist[r] + calc_dist(p[i].first, p[i].second, p[r].first, p[r].second);
                    pq.push(make_pair(dist[i], i));
                }
            }
        }
    }
    printf("%.015f\n", dist[Y]);
    return 0;
}