#pragma GCC optimize ("O3")
#pragma GCC target ("avx2")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define Would
#define you
#define please

#define PT pair<double, int>

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	int N, M, X, Y;
	cin >> N >> M >> X >> Y;

	int P[200001], Q[200001];
	rep1(i, N) {
		cin >> P[i] >> Q[i];
	}

	vector<PT> E[200001];
	rep1(i, M) {
		int p, q;
		cin >> p >> q;
		int x = (P[p] - P[q]);
		int y = (Q[p] - Q[q]);
		double d = sqrt(x * x + y * y);
		E[p].pb({ d, q });
		E[q].pb({ d, p });
	}

	double D[200001];
	rep1(i, N) D[i] = 1e18;
	D[X] = 0;

	priority_queue<PT, vector<PT>, greater<PT>> que;
	que.push(mp(0, X));

	while (que.size()) {
		PT p = que.top();
		que.pop();
		int i = p.second;
		if (D[i] != p.first) continue;
		for (PT p2 : E[i]) {
			int j = p2.second;
			double d = D[i] + p2.first;
			if (D[j] > d) {
				D[j] = d;
				que.push(mp(d, j));
			}
		}
	}

	cout << setprecision(12) << D[Y] << endl;

	Would you please return 0;
}