#include <bits/stdc++.h>
#define rep(i, a) for (int i = (int)0; i < (int)a; ++i)
#define rrep(i, a) for (int i = (int)a - 1; i >= 0; --i)
#define REP(i, a, b) for (int i = (int)a; i < (int)b; ++i)
#define RREP(i, a, b) for (int i = (int)a - 1; i >= b; --i)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
using ll = long long;
constexpr ll mod = 1e9 + 7;
constexpr ll INF = 1LL << 60;

template <class T>
inline bool chmin(T &a, T b)
{
	if (a > b)
	{
		a = b;
		return true;
	}
	return false;
}
template <class T>
inline bool chmax(T &a, T b)
{
	if (a < b)
	{
		a = b;
		return true;
	}
	return false;
}

ll gcd(ll n, ll m)
{
	ll tmp;
	while (m != 0)
	{
		tmp = n % m;
		n = m;
		m = tmp;
	}
	return n;
}

ll lcm(ll n, ll m)
{
	return abs(n) / gcd(n, m) * abs(m); //gl=xy
}

using namespace std;

template<typename T>
struct edge{
  int to;
  T cost;
  edge(int to,T cost):to(to),cost(cost){}
};


template<typename T>
vector<T> dijkstra(vector<vector<edge<T>>> &g,int s){//sは始点
  const auto INFTY=numeric_limits<T>::max();//2回以上使うときはオーバーフローに気をつける(INFTYのときはif文で弾くなど)
  vector<T>dist(g.size(),INFTY);
  using P=pair<T,int>;//firstは最短距離,secondは頂点の番号
  priority_queue<P,vector<P>,greater<P>>pq;
  dist[s]=0;
  pq.emplace(dist[s],s);

  while(!pq.empty()){
    auto x=pq.top();pq.pop();
    int v=x.second;
    if(dist[v]<x.first)continue;//最短距離でなければ飛ばす
    for(auto e:g[v]){
      if(dist[e.to]>dist[v]+e.cost){
        dist[e.to]=dist[v]+e.cost;
        pq.emplace(dist[e.to],e.to);
      }
    }
  }
  return dist;
}


void solve()
{
	int n, m;
	cin >> n >> m;
	int X, Y;
	cin >> X >> Y;
	X--;
	Y--;
	vector<pair<double, double>> p(n), P(m);
	rep(i, n) cin >> p[i].first >> p[i].second;
	rep(i, m) cin >> P[i].first >> P[i].second;
	vector<vector<edge<double>>> g(n);
	rep(i, m)
	{
		P[i].first--;
		P[i].second--;
		double x = P[i].first;
		double y = P[i].second;
		double d = sqrt(pow(p[x].first - p[y].first, 2) + pow(p[x].second - p[y].second, 2));
		g[x].eb(y, d);
		g[y].eb(x, d);
	}
	auto dd = dijkstra(g, X);
	cout << dd[Y] << endl;
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout << fixed << setprecision(15);
	solve();
	return 0;
}