#include "bits/stdc++.h"
using namespace std;

template<typename Type>
vector<Type> Dijkstra(vector<vector<pair<long long, Type> > > Graph, long long Start) {
	using PT = pair<Type, long long>;
	const Type Inf = numeric_limits<Type>::max();
	long long Size = Graph.size();
	vector<Type> Dist;
	Dist.assign(Size, Inf);
	priority_queue<PT, vector<PT>, greater<PT> > PQ;

	Dist[Start] = 0;
	PQ.emplace(PT(Dist[Start], Start));
	while (!PQ.empty()) {
		PT p = PQ.top();
		PQ.pop();
		Type D = p.first;
		long long E = p.second;
		if (Dist[E] < D) continue;
		for (pair<long long, Type> Next : Graph[E]) {
			Type ND = Next.second;
			long long NE = Next.first;
			if (Dist[NE] > Dist[E] + ND) {
				Dist[NE] = Dist[E] + ND;
				PQ.emplace(PT(Dist[NE], NE));
			}
		}
	}
	return Dist;
}

int main() {
	int N, M, X, Y;
	cin >> N >> M >> X >> Y;
	X--, Y--;
	vector<pair<double, double> > P(N);
	vector<vector<pair<long long, double> > > V(N);
	for (int i = 0; i < N; i++) {
		cin >> P[i].first >> P[i].second;
	}
	for (int i = 0; i < M; i++) {
		int S, T;
		cin >> S >> T;
		S--, T--;
		double D = (P[S].first - P[T].first) * (P[S].first - P[T].first) + (P[S].second - P[T].second) * (P[S].second - P[T].second);
		D = sqrt(D);
		V[S].push_back({ T, D });
		V[T].push_back({ S, D });
	}
	vector<double> Dist = Dijkstra(V, X);
	printf("%.12lf\n", Dist[Y]);
}