#include <algorithm>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
#define rep(i, n) for(int(i) = 0; (i) < (n); (i)++)
#define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++)
#define All(v) (v).begin(), (v).end()
#define pb push_back
#define MP(a, b) make_pair((a), (b))
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int INF = 1 << 30;
const ll LINF = 1LL << 60;
const int MOD = 1e9 + 7;

template <typename T> struct edge {
    int to;
    T cost;
    edge(int t, T c) : to(t), cost(c) {}
};

template <typename T> using Graph = vector<vector<edge<T>>>;

template <typename T> void dijkstra(int s, vector<T> &d, Graph<T> &G) {
    priority_queue<pair<int, T>, vector<pair<int, T>>, greater<pair<int, T>>>
        que;
    const auto INF = numeric_limits<T>::max();
    fill(All(d), INF);
    d[s] = 0;
    que.push(make_pair(0, s));
    while(!que.empty()) {
        pair<int, T> p = que.top();
        que.pop();
        int v = p.second;
        if(d[v] < p.first)
            continue;
        for(auto e : G[v]) {
            if(d[e.to] > d[v] + e.cost) {
                d[e.to] = d[v] + e.cost;
                que.push(make_pair(d[e.to], e.to));
            }
        }
    }
}

int main() {
    int N, M;
    cin >> N >> M;
    int X, Y;
    cin >> X >> Y;
    X--, Y--;
    vector<int> p(N), q(N);
    Graph<double> G(N);
    rep(i, N) { cin >> p[i] >> q[i]; }
    rep(i, M) {
        int P, Q;
        cin >> P >> Q;
        P--, Q--;
        double cost =
            sqrt((p[P] - p[Q]) * (p[P] - p[Q]) + (q[P] - q[Q]) * (q[P] - q[Q]));
        G[P].pb(edge<double>(Q, cost));
        G[Q].pb(edge<double>(P, cost));
    }
    vector<double> dist(N);
    dijkstra<double>(X, dist, G);
    cout << fixed << setprecision(10) << dist[Y] << endl;
    return 0;
}