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

//template
#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
typedef long long int ll;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
//end

typedef pair<int,int> P;
typedef pair<double,int> P2;

vector<P2> g[201010];

int main(){
   int n,m; cin>>n>>m;
   int s,t; cin>>s>>t; s--; t--;
   vector<P> pos(n); rep(i,0,n)cin>>pos[i].first>>pos[i].second;
   rep(i,0,m){
      int x,y; cin>>x>>y; x--; y--;
      double d=hypot(pos[x].first-pos[y].first,pos[x].second-pos[y].second);
      g[x].push_back({d,y}); g[y].push_back({d,x});
   }
   vector<double> dist(n,inf);
   dist[s]=0;
   priority_queue<P2,vector<P2>,greater<P2>> pq; pq.push({0,s});
   while(!pq.empty()){
      auto [d,v]=pq.top(); pq.pop();
      if(dist[v]<d)continue;
      for(auto [add,to]:g[v]){
         if(chmin(dist[to],d+add)){
            pq.push({dist[to],to});
         }
      }
   }
   printf("%.12f\n",dist[t]);
   return 0;
}