#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

const ll MOD = 1000000007;

struct Node {
  int v;
  double value;

  Node(int v = -1, double value = -1) {
    this->v = v;
    this->value = value;
  }

  bool operator>(const Node &n) const {
    return value > n.value;
  }
};

int main() {
  int N, M;
  cin >> N >> M;

  int X, Y;
  cin >> X >> Y;
  --X;
  --Y;

  vector<ll> P(N);
  vector<ll> Q(N);

  for (int i = 0; i < N; ++i) {
    cin >> P[i] >> Q[i];
  }

  vector<int> E[N + 1];
  for (int i = 0; i < M; ++i) {
    int p, q;
    cin >> p >> q;
    --p;
    --q;
    E[p].push_back(q);
    E[q].push_back(p);
  }

  priority_queue <Node, vector<Node>, greater<Node>> pque;
  pque.push(Node(X, 0));
  bool visited[N + 1];
  memset(visited, false, sizeof(visited));

  while (not pque.empty()) {
    Node node = pque.top();
    pque.pop();

    if (visited[node.v]) continue;
    visited[node.v] = true;

    // fprintf(stderr, "v: %d, dist: %f\n", node.v, node.value);

    if (node.v == Y) {
      cout << fixed << setprecision(10) << node.value << endl;
      break;
    }

    for (int u : E[node.v]) {
      ll dy = P[node.v] - P[u];
      ll dx = Q[node.v] - Q[u];
      double dist = sqrt(dy * dy + dx * dx);

      pque.push(Node(u, node.value + dist));
    }
  }
  

  return 0;
}