#include <bits/stdc++.h>
using namespace std;
int main(){
  cout << fixed << setprecision(5);
  int N, M;
  cin >> N >> M;
  int X, Y;
  cin >> X >> Y;
  X--;
  Y--;
  vector<int> p(N), q(N);
  for (int i = 0; i < N; i++){
    cin >> p[i] >> q[i];
  }
  vector<vector<pair<double, int>>> E(N);
  for (int i = 0; i < M; i++){
    int P, Q;
    cin >> P >> Q;
    P--;
    Q--;
    double d = hypot(p[Q] - p[P], q[Q] - q[P]);
    E[P].push_back(make_pair(d, Q));
    E[Q].push_back(make_pair(d, P));
  }
  vector<double> d(N, -1);
  priority_queue<pair<double, int>, vector<pair<double, int>>, greater<pair<double, int>>> pq;
  pq.push(make_pair(0, X));
  while (!pq.empty()){
    double c = pq.top().first;
    int v = pq.top().second;
    pq.pop();
    if (d[v] == -1){
      d[v] = c;
      for (auto P : E[v]){
        int w = P.second;
        if (d[w] == -1){
          pq.push(make_pair(c + P.first, w));
        }
      }
    }
  }
  cout << d[Y] << endl;
}