#include <bits/stdc++.h>
using namespace std;
#define INF_LL 100000000000000000LL
#define INF 200000000
#define MOD 1000000007
#define ll long long
#define all(x) x.begin(), x.end()
#define REP(i, a, b) for(int i = a; i < b; i++)
#define rep(i, n) REP(i, 0, n)
// typedef float double;
// typedef priority_queue prique;
typedef pair<double, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<P> vp;
typedef vector<ll> vl;
typedef vector<vi> matrix;
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
int sign[2] = {1, -1};
template <class T> bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return 1;
    }
    return 0;
}

ll modpow(ll a, ll b, ll m) {
    if(b == 0)
        return 1;
    ll t = modpow(a, b / 2, m);
    if(b & 1) {
        return (t * t % m) * a % m;
    } else {
        return t * t % m;
    }
}

// struct edge {
//     int to;
//     ll cost;
//     edge(int t, ll c) { to = t, cost = c; }
// };

struct edge {
    int to;
    double cost;
    edge(int t, double c) { to = t, cost = c; }
};

vector<double> dijkstra(vector<vector<edge>> &g, int start, int n) {
    priority_queue<P, vector<P>, greater<P>> que;
    vector<double> dist(n, INF_LL);
    dist[start] = 0;
    que.push(P(0, start));
    while(!que.empty()) {
        P p = que.top();
        que.pop();
        int v = p.second;
        if(dist[v] < p.first)
            continue;
        rep(i, (int)g[v].size()) {
            edge e = g[v][i];
            if(dist[e.to] > dist[v] + e.cost) {
                dist[e.to] = dist[v] + e.cost;
                que.push(P(dist[e.to], e.to));
            }
        }
    }
    return dist;
}

signed main() {
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    x--;
    y--;
    vector<pair<int, int>> a(n);
    rep(i, n) cin >> a[i].first >> a[i].second;
    vector<vector<edge>> g(n);
    rep(i, m) {
        int p, q;
        cin >> p >> q;
        double t = sqrt((a[p - 1].first - a[q - 1].first) *
                            (a[p - 1].first - a[q - 1].first) +
                        (a[p - 1].second - a[q - 1].second) *
                            (a[p - 1].second - a[q - 1].second));
        g[p - 1].push_back({q - 1, t});
        g[q - 1].push_back({p - 1, t});
    }
    vector<double> dist = dijkstra(g, x, n);
    cout << fixed << setprecision(15) << dist[y] << endl;
    return 0;
}