#include <bits/stdc++.h>
using namespace std;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
using Int = long long;
const char newl = '\n';


template<typename T>
struct Dijkstra{
  struct Edge{
    int to;
    T cost;
    Edge(int to,T cost):to(to),cost(cost){}
    bool operator<(const Edge &o)const{return cost>o.cost;}
  };

  vector< vector<Edge> > G;
  vector<T> ds;
  vector<int> bs;
  Dijkstra(int n):G(n){}

  void add_edge(int u,int v,T c){
    G[u].emplace_back(v,c);
  }

  void build(int s){
    int n=G.size();
    ds.assign(n,numeric_limits<T>::max());
    bs.assign(n,-1);

    priority_queue<Edge> pq;
    ds[s]=0;
    pq.emplace(s,ds[s]);

    while(!pq.empty()){
      auto p=pq.top();pq.pop();
      int v=p.to;
      if(ds[v]<p.cost) continue;
      for(auto e:G[v]){
        if(ds[e.to]>ds[v]+e.cost){
          ds[e.to]=ds[v]+e.cost;
          bs[e.to]=v;
          pq.emplace(e.to,ds[e.to]);
        }
      }
    }
  }

  T operator[](int k){return ds[k];}

  vector<int> restore(int to){
    vector<int> res;
    if(bs[to]<0) return res;
    while(~to) res.emplace_back(to),to=bs[to];
    reverse(res.begin(),res.end());
    return res;
  }
};


struct Precision{
  Precision(){
    cout<<fixed<<setprecision(12);
  }
}precision_beet;

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);

  int n,m;
  cin>>n>>m;
  int x,y;
  cin>>x>>y;
  x--;y--;

  using D = double;
  vector<D> ps(n),qs(n);
  for(int i=0;i<n;i++) cin>>ps[i]>>qs[i];

  Dijkstra<D> G(n);
  for(int i=0;i<m;i++){
    int u,v;
    cin>>u>>v;
    u--;v--;
    D d=hypot(ps[u]-ps[v],qs[u]-qs[v]);
    G.add_edge(u,v,d);
    G.add_edge(v,u,d);
  }

  G.build(x);
  cout<<G[y]<<newl;
  return 0;
}