#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 10000000000000000.0

double eps = 1e-7;

int main(){
	
	int N,M,X,Y;
	cin>>N>>M>>X>>Y;
	
	X--;Y--;
	
	vector<double> x(N),y(N);
	for(int i=0;i<N;i++)cin>>x[i]>>y[i];
	
	vector<vector<pair<int,double>>> E(N,vector<pair<int,double>>());
	
	for(int i=0;i<M;i++){
		int u,v;
		cin>>u>>v;
		u--;v--;
		double d = sqrt(pow(x[u]-x[v],2.0)+pow(y[u]-y[v],2.0));
		E[u].emplace_back(v,d);
		E[v].emplace_back(u,d);
	}
	
	vector<double> dis(N,Inf);
	vector<bool> visited(N,false);
	priority_queue<pair<double,int>,vector<pair<double,int>>,greater<pair<double,int>>> Q;
	Q.emplace(0.0,X);
	dis[X] = 0.0;
	
	while(Q.size()!=0){
		double D1 = Q.top().first;
		int from = Q.top().second;
		Q.pop();
		if(visited[from])continue;
		if(abs(dis[from]-D1)>eps)continue;
		visited[from]=true;
		for(int i=0;i<E[from].size();i++){
			int to = E[from][i].first;
			if(visited[to])continue;
			double D2 = E[from][i].second;
			if(dis[to]>D1+D2+eps){
				dis[to] = D1+D2;
				Q.emplace(dis[to],to);
			}
		}
	}
	
	cout<<fixed<<setprecision(10)<<dis[Y]<<endl;
	
	return 0;
}