#include <bits/stdc++.h>
using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define DEBUG(...)
#endif

template <class T> struct graph {
  struct edge {
    int to;
    T w;
    operator int() const { return to; }
  };
  template <class It> struct edge_list {
    const It bg, ed;
    It begin() const { return bg; }
    It end() const { return ed; }
    auto&& operator[](size_t i) const { return bg[i]; }
    size_t size() const { return ed - bg; }
  };
  vector<pair<int, edge>> pool;
  vector<int> head;
  vector<edge> edges;
  graph(int n) : head(n + 1) {}
  void add(int from, int to, T w = 1) {
    pool.push_back({from, {to, w}});
    ++head[from];
  }
  void build() {
    partial_sum(begin(head), end(head), begin(head));
    edges.resize(head.back());
    while (not empty(pool)) {
      edges[--head[pool.back().first]] = pool.back().second;
      pool.pop_back();
    }
    decltype(pool)().swap(pool);
  }
  edge_list<class vector<edge>::const_iterator> operator[](int v) const {
    return {begin(edges) + head[v], begin(edges) + head[v + 1]};
  }
  edge_list<class vector<edge>::iterator> operator[](int v) {
    return {begin(edges) + head[v], begin(edges) + head[v + 1]};
  }
  size_t size() const { return std::size(head) - 1; }
};

template <class T> constexpr T inf = numeric_limits<T>::max() / 2.1;

auto chmin = [](auto&& a, auto b) { return b < a ? a = b, 1 : 0; };

template <class T, class G> auto dijkstra(const G& g, int s) {
  vector d(size(g), inf<T>);
  vector prv(size(g), -1);
  priority_queue<pair<T, int>, vector<pair<T, int>>, greater<>> rh;
  rh.emplace(d[s] = 0, s);
  while (not empty(rh)) {
    auto [dv, v] = rh.top();
    rh.pop();
    if (dv != d[v]) continue;
    for (auto&& e : g[v])
      if (chmin(d[e.to], dv + e.w)) {
        rh.emplace(d[e.to], e.to);
        prv[e.to] = v;
      }
  }
  return make_pair(d, prv);
}

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);
  int n, m, s, t;
  cin >> n >> m >> s >> t;
  --s, --t;
  vector<double> x(n), y(n);
  for (int i = 0; i < n; ++i) {
    cin >> x[i] >> y[i];
  }
  graph<double> g(n);
  while (m--) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    double w = hypot(x[v] - x[u], y[v] - y[u]);
    g.add(u, v, w);
    g.add(v, u, w);
  }
  g.build();
  cout << dijkstra<double>(g, s).first[t] << '\n';
}