#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i ++)
using namespace std;
typedef long long ll;
typedef pair<double,int> PL;
typedef pair<int,int> P;
const int INF = 1e9;
const ll MOD = 1e12;
const double eps = 1e-6;

vector<double> dijkstra(int n, vector<vector<PL>>& G,int& s) {
    vector<double> dist(n,(double)INF);
    dist[s] = 0.0;

    priority_queue<PL,vector<PL>,greater<P>> q;
    q.push({0.0,s});

    while (!q.empty()) {
        PL p = q.top(); q.pop();
        double d = p.first;
        int v = p.second;
        if (dist[v] < d) continue;
        for (PL p: G[v]) {
            double cost = p.first;
            int e = p.second;
            if (dist[e] > dist[v] + cost) {
                dist[e] = dist[v] + cost;
                q.push({dist[e],e});
            }
        }  
    }
    return dist;
}

int main() {
    int N,M,X,Y; cin >> N >> M >> X >> Y; X--;Y--;
    vector<pair<int,int>> point(N);
    rep(i,N) cin >> point[i].first >> point[i].second;
    vector<vector<PL>> G(N);
    auto dist = [&](int x,int y){return sqrt((point[x].first - point[y].first) * (point[x].first - point[y].first) + (point[x].second - point[y].second) * (point[x].second - point[y].second));};
    rep(_,M){
        int p,q; cin >> p >> q;
        p --; q --;
        double d = dist(p,q);
        G[p].push_back(PL(d,q));
        G[q].push_back(PL(d,p));
    }
    vector<double> distance = dijkstra(N,G,X);
    double ans = distance[Y];
    printf("%0.10f\n",ans);
}