#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;
constexpr int INF = 2e9;
typedef long double ld;
int main() {
  int n, m;
  cin >> n >> m;
  int x, y;
  cin >> x >> y;
  x--; y--;
  vector<pair<ld, ld>> p;
  rep(i,n) {
    ld a, b;
    cin >> a >> b;
    p.emplace_back(make_pair(a, b));
  }
  vector<vector<pair<int, ld>>> g(n);
  rep(i,m) {
    int u, v;
    cin >> u >> v;
    u--; v--;
    ld s = (p[u].first - p[v].first), t = (p[u].second - p[v].second);
    ld d = sqrt((s * s) + (t * t));
    g[u].emplace_back(make_pair(v, d));
    g[v].emplace_back(make_pair(u, d));
  }

  vector<ld> dist(n, INF);
  priority_queue<pair<ld, int>, vector<pair<ld, int>>, greater<pair<ld, int>>> pq;
  pq.push(make_pair(0.0, x));
  dist[x] = 0.0;

  while (!pq.empty()) {
    auto t = pq.top();
    pq.pop();
    int u = t.second;
    if (t.first > dist[u]) continue;
    for (auto e : g[u]) {
      ld cost = e.second;
      int v = e.first;
      if (dist[v] > dist[u] + cost) {
        dist[v] = dist[u] + cost;
        pq.push(make_pair(dist[v], v));
      } 
    }
  }

  printf("%.12Lf\n", dist[y]);
  return 0;
}