#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

using CostType = double;
struct Edge {
  int src, dst; CostType cost;
  Edge(int src, int dst, CostType cost = 0) : src(src), dst(dst), cost(cost) {}
  inline bool operator<(const Edge &x) const {
    return cost != x.cost ? cost < x.cost : dst != x.dst ? dst < x.dst : src < x.src;
  }
  inline bool operator<=(const Edge &x) const { return !(x < *this); }
  inline bool operator>(const Edge &x) const { return x < *this; }
  inline bool operator>=(const Edge &x) const { return !(*this < x); }
};

struct Dijkstra {
  using Pci = pair<CostType, int>;

  Dijkstra(const vector<vector<Edge>> &graph, const CostType CINF) : graph(graph), CINF(CINF) {}

  vector<CostType> build(int s) {
    int n = graph.size();
    vector<CostType> dist(n, CINF);
    dist[s] = 0;
    prev.assign(n, -1);
    priority_queue<Pci, vector<Pci>, greater<Pci>> que;
    que.emplace(0, s);
    while (!que.empty()) {
      CostType cost; int ver; tie(cost, ver) = que.top(); que.pop();
      if (dist[ver] < cost) continue;
      for (const Edge &e : graph[ver]) {
        if (dist[e.dst] > dist[ver] + e.cost) {
          dist[e.dst] = dist[ver] + e.cost;
          prev[e.dst] = ver;
          que.emplace(dist[e.dst], e.dst);
        }
      }
    }
    return dist;
  }

  vector<int> build_path(int t) {
    vector<int> res;
    for (; t != -1; t = prev[t]) res.emplace_back(t);
    reverse(ALL(res));
    return res;
  }

private:
  vector<vector<Edge>> graph;
  const CostType CINF;
  vector<int> prev;
};

int main() {
  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];
  vector<vector<Edge>> graph(n);
  while (m--) {
    int P, Q; cin >> P >> Q; --P; --Q;
    double dist = sqrt((p[P] - p[Q]) * (p[P] - p[Q]) + (q[P] - q[Q]) * (q[P] - q[Q]));
    graph[P].emplace_back(P, Q, dist);
    graph[Q].emplace_back(Q, P, dist);
  }
  Dijkstra dij(graph, LINF);
  cout << dij.build(x)[y] << '\n';
  return 0;
}