#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <iostream>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <random>
#include <set>
#include <queue>
#define REP(i, n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
constexpr ll INF = 1LL << 60;

int n, m, x, y;

// O(|V|+|E|)log|V|)
void dijkstra(int s, vector<vector<pair<int, double>>> &g, vector<double> &dist)
{
  using Info = pair<double, int>;
  // init
  dist.assign(g.size(), 1e18);
  dist[s] = 0.0;
  priority_queue<Info, vector<Info>, greater<Info>> pq;
  pq.emplace(0.0, s);
  //
  // main
  while (!pq.empty())
  {
    double d = pq.top().first;
    int v = pq.top().second;
    pq.pop();
    if (dist[v] < d)
      continue;
    for (auto e : g[v])
    {
      if (dist[e.first] > dist[v] + e.second)
      {
        dist[e.first] = dist[v] + e.second;
        pq.emplace(dist[e.first], e.first);
      }
    }
  }
  //
}

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

  cin >> n >> m >> x >> y;
  --x, --y;
  vector<pair<double, double>> pos;
  REP(i, n)
  {
    double p, q;
    cin >> p >> q;
    pos.emplace_back(p, q);
  }

  vector<vector<pair<int, double>>> g(n);
  REP(i, m)
  {
    int p, q;
    cin >> p >> q;
    --p, --q;
    double X = pos[p].first - pos[q].first;
    double Y = pos[p].second - pos[q].second;
    double cost = sqrt(X * X + Y * Y);
    g[q].emplace_back(p, cost);
    g[p].emplace_back(q, cost);
  }

  vector<double> dist;
  dijkstra(x, g, dist);
  cout << fixed << setprecision(10) << dist[y] << '\n';

  return 0;
}