#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

#define MAX_N 200005
struct Edge {
  int src, dest;
  double weight;
};
bool operator>(const Edge& a, const Edge& b){
  return a.weight > b.weight;
}
int N, M;
vector<Edge> G[MAX_N];
double cost[MAX_N];

void dijkstra(int start){
  rep(i,N+1){
    cost[i] = 1e100;
  }
  priority_queue<Edge,vector<Edge>,greater<Edge>> q;
  q.push((Edge){-1,start,0});

  while(!q.empty()){
    Edge e=q.top();
    q.pop();
    if(cost[e.dest] < 1e99) continue;
    cost[e.dest]=e.weight;
    FOR(it,G[e.dest])
      if(cost[it->dest] > 1e99) q.push((Edge){it->src,it->dest,e.weight+it->weight});
  }
}

int main(){
  cin >> N >> M;
  int X, Y;
  cin >> X >> Y;
  vector<pair<int,int>> v;
  v.emplace_back(0,0);
  rep(i,N){
    int p, q;
    cin >> p >> q;
    v.emplace_back(p,q);
  }
  rep(i,M){
    int p, q;
    cin >> p >> q;

    double px = v[p].first;
    double py = v[p].second;
    double qx = v[q].first;
    double qy = v[q].second;
    double dist = sqrt((px-qx)*(px-qx) + (py-qy)*(py-qy));
    G[p].push_back((Edge){p,q,dist});
    G[q].push_back((Edge){q,p,dist});
  }

  dijkstra(X);
  double ret = cost[Y];
  printf("%.12lf\n", ret);
  
  return 0;
}