#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<double,int>;
vector<ll> g[2*100000];
vector<pair<ll,ll>> vp;
double G[200000];
int n,m;
int X,Y;

int main()
{
	cin >> n >> m;
	cin >> X >> Y;
	X--;Y--;
	for(int i = 0;i < n;i++)
	{
		int x,y;
		cin >> x >> y;
		vp.emplace_back(x,y);
	}
	for(int i = 0;i<m;i++)
	{
		int x,y;
		cin >> x >> y;
		x--;y--;
		g[x].push_back(y);
		g[y].push_back(x);
	}
	for(int i =0;i<200000;i++)
	{
		G[i] = 1e9;
	}
	priority_queue<P,vector<P>,greater<P>>PQ;
	G[X] = 0.0;
	PQ.emplace(0.0,X);

	while(!PQ.empty())
	{
		auto now = PQ.top();
		PQ.pop();
		int v = now.second;
		//cout<<v<<endl;
		if(G[v]!=now.first)continue;
		//cout<<v<<endl;
		for(auto i: g[v])
		{
			double div = sqrt((vp[i].first-vp[v].first)*(vp[i].first-vp[v].first)+(vp[i].second-vp[v].second)*(vp[i].second-vp[v].second));
			if(G[i]>G[v]+div)
			{
				G[i]=G[v]+div;
				PQ.emplace(G[i],i);
			}
		}
	}
	printf("%.7lf\n",G[Y]);

}