#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<queue>
#include<utility>

using namespace std;

#define int long long
#define endl "\n"

constexpr long long INF = (long long)1e18;
constexpr long long MOD = 1'000'000'007; 

struct fast_io {
	fast_io(){
		std::cin.tie(nullptr);
		std::ios::sync_with_stdio(false);
	};
} fio;


void dijkstra(int s, vector<long double> &d, vector<vector<pair<int,long double>>> &G){
	priority_queue<pair<long double,int>,vector<pair<long double,int>>,greater<pair<long double,int>>> q;
	
	d.clear();
	d.resize(G.size(),INF);
	d[s] = 0;
	q.push(make_pair(0,s));
	
	while(!q.empty()){
		pair<long double,int> p = q.top();q.pop();
		int v = p.second;
		
		if(d[v] < p.first) continue;
		
		for(pair<int,long double> e : G[v]){
			if(d[e.first] > d[v] + e.second){
				d[e.first] = d[v] + e.second;
				q.push(make_pair(d[e.first],e.first));
			}
		}
	}	
}

long double dis(vector<pair<int,int>> &p, int a, int b){
	long double x = (p[a].first - p[b].first);
	long double y = (p[a].second - p[b].second);
	
	return sqrt(x * x + y * y);
}

signed main(){
	cout<<fixed<<setprecision(10);
	
	int N, M;
	int X, Y;
	vector<pair<int,int>> p;
	vector<vector<pair<int,long double>>> G;
	vector<long double> d; 
	cin>>N>>M;
	
	cin>>X>>Y;
	
	X--, Y--;
	
	p.resize(N);
	G.resize(N);
	
	for(int i = 0; i < N; i++){
		cin>>p[i].first>>p[i].second;
	}
	
	for(int i = 0; i < M; i++){
		int P, Q;
		
		cin>>P>>Q;
		
		P--, Q--;
		
		G[P].push_back({Q, dis(p, P, Q)});
		G[Q].push_back({P, dis(p, P, Q)});
	}
	
	dijkstra(X, d, G);
	
	
	cout<<d[Y]<<endl;
	
	return 0;
}