#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N, M, X, Y;
	cin >> N >> M >> X >> Y;
	--X; --Y;
	vector<int> y(N), x(N);
	REP(i, N) scanf("%d %d", &y[i], &x[i]);
	vector<vector<pair<int, double>>> g(N);
	REP(i, M) {
		int P, Q;
		scanf("%d %d", &P, &Q);
		--P; --Q;
		const double l = hypot(x[P] - x[Q], y[P] - y[Q]);
		g[P].emplace_back(Q, l);
		g[Q].emplace_back(P, l);
	}
	
	using tup = tuple<double, int>;
	vector<double> dist(N, INF);
	priority_queue<tup, vector<tup>, greater<tup>> pq;
	dist[X] = 0;
	pq.emplace(0, X);
	while (!pq.empty()) {
		auto [d, u] = pq.top(); pq.pop();
		if (dist[u] != d) continue;
		for (auto [v, c] : g[u]) if (chmin(dist[v], d + c)) pq.emplace(dist[v], v);
	}
	printf("%.18f\n", dist[Y]);
}