#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);
const double INF = 1e100;

vector<pair<int, double> > edges[200000];
double dist[200000];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n, m, x, y;
  cin >> n >> m >> x >> y;
  --x, --y;

  vector<int> p(n), q(n);
  REP (i, n) cin >> p[i] >> q[i];

  REP (i, m) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    double dist = hypot(abs(p[u]-p[v]), abs(q[u]-q[v]));
    edges[u].emplace_back(v, dist);
    edges[v].emplace_back(u, dist);
  }
  
  REP (i, 200000) dist[i] = INF;
  priority_queue<pair<double, int>, vector<pair<double, int>>, greater<pair<double, int>> > Q;
  dist[x] = 0.0;
  Q.emplace(dist[x], x);

  while (!Q.empty()) {
    int v;
    double w;
    tie(w, v) = Q.top();
    Q.pop();
    for (auto &[u, d]: edges[v]) {
      if (dist[v] + d < dist[u]) {
        dist[u] = dist[v] + d;
        Q.emplace(dist[u], u);
      }
    }
  }

  cout << fixed << setprecision(6) << dist[y] << endl;

  return 0;
}