#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

int main()
{
	int n, m;
	cin>>n>>m;
	int x, y; cin>>x>>y; x--; y--;
	double a[200020], b[200020];
	for(int i=0; i<n; i++) cin>>a[i]>>b[i];
	using Pd=pair<double, int>;
	vector<Pd> g[200020];
	for(int i=0; i<m; i++){
		int p, q; cin>>p>>q;
		p--; q--;
		double d=sqrt((a[p]-a[q])*(a[p]-a[q])+(b[p]-b[q])*(b[p]-b[q]));
		g[p].push_back({d, q});
		g[q].push_back({d, p});
	}
	priority_queue<Pd, vector<Pd>, greater<Pd>> que;
	double d[200020];
	const double INF=1e18;
	fill(d, d+n, INF);
	d[x]=0;
	que.push({0, x});
	while(!que.empty()){
		auto p=que.top(); que.pop();
		int s=p.second;
		if(d[s]<p.first) continue;
		for(auto q:g[s]){
			int t=q.second;
			if(d[t]>d[s]+q.first){
				d[t]=d[s]+q.first;
				que.push({d[t], t});
			}
		}
	}
	printf("%.12lf\n", d[y]);
	return 0;
}