#include <iostream>
#include <iomanip>
#include <cmath>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <numeric>
#include <random>
#include <algorithm>
#include <functional>

using namespace std;
typedef long long ll;

const int INF = (1 << 30) - 1;
const ll INFLL= (1LL << 61) - 1;
const int MOD = 1000000007;
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

using namespace std;

template<class T>
struct Edge {
  int to;
  T cost;
  Edge() {}
  Edge(int to, T cost) : to(to), cost(cost) {}
  bool operator>(const Edge &r) const { return this->cost > r.cost; }
};

template<class T>
vector<T> Dijkstra(const vector<vector<Edge<T>>> &edges, const int st) {

  const int V = (int)edges.size();
  const T inf = numeric_limits<T>::max() / 2;
  vector<T> cost(V, inf);
  cost[st] = 0;

  priority_queue<Edge<T>, vector<Edge<T>>, greater<Edge<T>>> pq;
  pq.emplace(st, cost[st]);

  while (!pq.empty()) {

    Edge<T> now(pq.top().to, pq.top().cost);
    pq.pop();

    if (cost[now.to] < now.cost) continue;
    for (const Edge<T> &e : edges[now.to]) {
      T tmp_cost = now.cost + e.cost;
      if (cost[e.to] > tmp_cost) {
        cost[e.to] = tmp_cost;
        pq.emplace(e.to, cost[e.to]);
      }
    }
  }

  return cost;
}

template<class T> inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template<class T> inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}


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

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

  vector<long double>p(N),q(N);
  REP(i,N){
    cin>>p[i]>>q[i];
  }
  vector<vector<Edge<long double>>> edges(N);

  REP(i,M){
    int P,Q;
    cin>>P>>Q;
    P--;Q--;
    long double len=sqrtl((p[P]-p[Q])*(p[P]-p[Q]) + (q[P]-q[Q])*(q[P]-q[Q]));
    edges[P].emplace_back(Q,len);
    edges[Q].emplace_back(P,len);
  }

  auto ans = Dijkstra<long double>(edges,X);

  cout<<setprecision(15)<<ans[Y]<<endl;
}