/*
confirm 0LL and 1LL
confirm cornercases such as 0
confirm times of cin < 10^6
*/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
using Graph = vector<VecP>;
template <typename T>
using Vec1 = vector<T>;
template <typename T>
using Vec2 = vector<Vec1<T> >;
#define REP(i, m, n) for(ll i = (m); (i) < (n); ++(i))
#define REPN(i, m, n) for(ll i = (m); (i) <= (n); ++(i))
#define REPR(i, m, n) for(ll i = (m)-1; (i) >= (n); --(i))
#define REPNR(i, m, n) for(ll i = (m); (i) >= (n); --(i))
#define rep(i, n) REP(i, 0, n)
#define repn(i, n) REPN(i, 1, n)
#define repr(i, n) REPR(i, n, 0)
#define repnr(i, n) REPNR(i, n, 1)
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define fs first
#define sc second
template <typename T>
bool chmax(T &a, const T b){if(a < b){a = b; return true;} return false;}
template <typename T>
bool chmin(T &a, const T b){if(a > b){a = b; return true;} return false;}
template <typename T>
ll pow2(const T n){return (1LL << n);}
template <typename T>
void cosp(const T n){cout << n << ' ';}
void co(void){cout << '\n';}
template <typename T>
void co(const T n){cout << n << '\n';}
template <typename T1, typename T2>
void co(pair<T1, T2> p){cout << p.fs << ' ' << p.sc << '\n';}
template <typename T>
void co(const Vec1<T> &v){for(T i : v) cosp(i); co();}
template <typename T>
void co(initializer_list<T> v){for(T i : v) cosp(i); co();}
template <typename T>
void ce(const T n){cerr << n << endl;}
void sonic(){ios::sync_with_stdio(false); cin.tie(0);}
void setp(const ll n){cout << fixed << setprecision(n);}
constexpr int INF = 1e9+1;
constexpr ll LINF = 1e18+1;
constexpr ll MOD = 1e9+7;
//constexpr ll MOD = 998244353;
constexpr ld EPS = 1e-11;
const ld PI = acos(-1);

vector<vector<pair<ld, ll>>> graph;
vector<ld> dist;

void dijkstra(ll s){
	using Pd = pair<ld, ll>;
	priority_queue<Pd, vector<Pd>, greater<Pd> > que;
	que.push({0, s});
	while(!que.empty()){
		Pd o = que.top(); que.pop();
		if(o.fs >= dist[o.sc]) continue;
		dist[o.sc] = o.fs;
		for(Pd i : graph[o.sc]) que.push({o.fs+i.fs, i.sc});
	}
}

ld getDist(ll p, ll q, VecP &pos){
	return sqrt((ld)pow(pos[p].fs - pos[q].fs, 2) + pow(pos[p].sc - pos[q].sc, 2));
}

int main(void){
	ll n, m, x, y;
	cin >> n >> m >> x >> y;
	graph.resize(n);
	dist.assign(n, LINF);
	--x, --y;
	VecP pos(n);
	rep(i, n) cin >> pos[i].fs >> pos[i].sc;

	rep(i, m){
		ll p, q;
		cin >> p >> q;
		--p, --q;
		graph[p].pb({getDist(p, q, pos), q});
		graph[q].pb({getDist(p, q, pos), p});
	}

	dijkstra(x);
	setp(10);
	co(dist[y]);

	return 0;
}