#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <cstdio>
#include <cmath>
#include <tuple>
#include <iomanip>
#include <numeric>
#include <unordered_map>
#include <sstream>
#include<limits.h>
#include<float.h>
#include<list>
#include <array>
#include <complex>
#include<stdio.h>
#include<string.h>
#include <bitset>
#include<assert.h>

using namespace std;
#define int long long

#define I32_MAX 2147483647
#define I64_MAX 9223372036854775807LL
#define I64_MAX2 1223372036854775807LL
#define INF I64_MAX2
#define MOD 1000000007
#define MEM_SIZE 10000
#define DEBUG_OUT true
#define ALL(x) (x).begin(), (x).end()

template<typename T> void DEBUG(T e){if(DEBUG_OUT == false)return; std::cout << e <<" ";}
template<typename T> void DEBUG(const std::vector<T>& v){if(DEBUG_OUT == false)return;for(const auto& e : v){std::cout<< e << " "; } std::cout << std::endl;}
template<typename T> void DEBUG(const std::vector<std::vector<T> >& vv){if(DEBUG_OUT == false)return;for(const auto& v : vv){ DEBUG(v); } }
template<class T,class... Ts> void DEBUG(T d, Ts... e){if(DEBUG_OUT == false)return;DEBUG(d);DEBUG(e...);}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; abort();}}
template< typename T1, typename T2 > inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template< typename T1, typename T2 > inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T >
struct edge {
  int src, to;
  T cost;
 
  edge(int to, T cost) : src(-1), to(to), cost(cost) {}
 
  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}
 
  edge &operator=(const int &x) {
    to = x;
    return *this;
  }
 
  operator int() const { return to; }
};
 
template< typename T >
using Edges = vector< edge< T > >;
template< typename T >
using WeightedGraph = vector< Edges< T > >;
using UnWeightedGraph = vector< vector< int > >;
template< typename T >
using Matrix = vector< vector< T > >;
 
template< typename T >
vector< T > dijkstra(WeightedGraph< T > &g, int s) {
  const auto INF1 = numeric_limits< T >::max();
  vector< T > dist(g.size(), INF1);

  using Pi = pair< T, int >;
  priority_queue< Pi, vector< Pi >, greater< Pi > > que;
  dist[s] = 0;
  que.emplace(dist[s], s);
  while(!que.empty()) {
    T cost;
    int idx;
    tie(cost, idx) = que.top();
    que.pop();
    if(dist[idx] < cost) continue;
    for(auto &e : g[idx]) {
      auto next_cost = cost + e.cost;
      if(dist[e.to] <= next_cost) continue;
      dist[e.to] = next_cost;
      que.emplace(dist[e.to], e.to);
    }
  }
  return dist;
}


void solve(void)
{
  int N,M;
  cin>>N>>M;
  int S,G;
  cin>>S>>G;
  S--;G--;
  vector<pair<double,double> > vp;
  for (int i = 0; i < N; i++)
  {
    double X,Y;cin>>X>>Y;
    vp.push_back(make_pair(X,Y));
  }
  WeightedGraph<double> WG (N);
  for (int i = 0; i < M; i++)
  {
    int P,Q;
    cin>>P>>Q;
    P--;Q--;
    double D = sqrt(pow(vp[P].first - vp[Q].first ,2 ) + pow(vp[P].second - vp[Q].second ,2 ));
    WG[P].emplace_back(P,Q,D);
    WG[Q].emplace_back(Q,P,D);
  }
  auto path = dijkstra(WG,S);
  cout<<path[G]<<endl;
  

  
  return;
}
int32_t main(int32_t argc, const char *argv[])
{
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  std::cout << std::fixed;
  std::cout << std::setprecision(11);
  solve();

  return 0;
}