#define _GLIBCXX_DEBUG
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define ALL(v) v.begin(), v.end()
typedef long long ll;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#include <bits/stdc++.h>
using namespace std;

#define MAX 200010
#define INF 1000100100
vector<pair<int,double>> vec[MAX];
double d[MAX],color[MAX],p[MAX],q[MAX];
int n,m,x,y;

void dijk(int s){
  priority_queue<pair<double,int>> pq;
  for(int i=1;i<=n;i++){
    d[i]=INF;
    color[i]=0;
  }
  d[s]=0;
  pq.push({0,s});
  color[s]=1;
  
  while(!pq.empty()){
    pair<double,int> f=pq.top(); pq.pop();
    int u=f.second;
    color[u]=2;
    
    if(d[u]<f.first*(-1)) continue;
    
    for(int j=0;j<vec[u].size();j++){
      int v=vec[u][j].first;
      if(color[v]==2) continue;
      if(d[v] > d[u]+vec[u][j].second){
        d[v]=d[u]+vec[u][j].second;
        pq.push({d[v]*(-1),v});
        color[v]=1;
      }
    }
  }
                     
}


int main() {
  cin>>n>>m>>x>>y;
  
  int a,b;
  double c;
  rep(i,n) cin>>p[i+1]>>q[i+1];
  rep(i,m){
    cin>>a>>b;
    c=sqrt((p[a]-p[b])*(p[a]-p[b])+(q[a]-q[b])*(q[a]-q[b]));
    vec[a].push_back({b,c});
    vec[b].push_back({a,c});
  }
  
  dijk(x);
  cout<< fixed << setprecision(15) <<d[y]<<endl;
  
  return 0;
}