#include <iostream>
#include <string>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <ctime>
#include <queue>
#include <stack>
#include <functional>
#include <bitset>
#include <assert.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(ll i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = 1<<30;
const ll linf = 1LL<<62;
const int MAX = 510000;
ll dy[8] = {0,1,0,-1,1,-1,1,-1};
ll dx[8] = {1,0,-1,0,1,-1,-1,1};
const double pi = acos(-1);
const double eps = 1e-7;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    rep(i,a.size()) cout << a[i] << " ";
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){cout << a << " " << b << "\n";}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
const int mod = 1e9 + 7;
//const int mod = 998244353;

double dist(ll a, ll b, ll c, ll d){
	double res = sqrt((a-c)*(a-c) + (b-d)*(b-d));
	return res;
}

typedef pair<double, ll> pd;

int main(){
	ll n,m; cin >> n >> m;
	ll x,y; cin >> x >> y; x--; y--;
	vvl G(n);
	vl p(n), q(n);
	rep(i,n){
		cin >> p[i] >> q[i];
	}
	rep(i,m){
		ll u,v; cin >> u >> v; u--; v--;
		G[u].push_back(v);
		G[v].push_back(u);
	}
	vd d(n,linf);
	d[y] = 0;
	priority_queue<pd, vector<pd>, greater<pd>> pq;
	pq.emplace(0.0,y);
	while(!pq.empty()){
		pd pp = pq.top(); pq.pop();
		ll u = pp.second;
		if(d[u] < pp.first) continue;
		for(auto v : G[u]){
			double di = dist(p[u],q[u],p[v],q[v]);
			if(d[v] > d[u] + di){
				d[v] = d[u] + di;
				pq.emplace(d[v], v);
			}
		}
	}
	printf("%.10f\n",d[x]);
}