#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define rrep(i,n) for(int i=1;i<(n);++i)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define maxs(a, b) a = max(a, b)
#define mins(a, b) a = min(a, b)
using namespace std;
typedef long long ll;
typedef pair<double, int> P;
const ll linf = (1ll << 61);
const int inf = 1001001001;
const int mod = 1000000007;

struct edge { int to; double cost; };
vector<edge> g[200005];
int n, m;
int X, Y;
double d[200005];

double dijkstra() {
	priority_queue<P, vector<P>, greater<P>> pq;
	fill(d, d + n, inf);
	d[X] = 0;
	pq.emplace(0, X);
	while (pq.size()) {
		P p = pq.top(); pq.pop();
		int v = p.second;
		if (d[v] < p.first) continue;
		for (auto& c : g[v]) {
			edge e = c;
			if (d[e.to] > d[v] + e.cost) {
				d[e.to] = d[v] + e.cost;
				pq.emplace(d[e.to], e.to);
			}
		}
	}
	return d[Y];
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> n >> m;
	cin >> X >> Y;
	X--; Y--;
	vector<int> p(n), q(n);
	rep(i, n) cin >> p[i] >> q[i];
	rep(i, m) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		g[a].push_back({ b, sqrt(pow(abs(p[a] - p[b]), 2) + pow(abs(q[a] - q[b]), 2)) });
		g[b].push_back({ a, sqrt(pow(abs(p[a] - p[b]), 2) + pow(abs(q[a] - q[b]), 2)) });
	}
	double ans = dijkstra();
	printf("%.10f\n", ans);
 	return 0;
}