#include <bits/stdc++.h>
#define FASTIO
using namespace std;

using ll = long long;
using Vi = vector<int>;
using Vl = vector<ll>;
using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

constexpr int I_INF = numeric_limits<int>::max();
constexpr ll L_INF = numeric_limits<ll>::max();

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

struct Pos {
    double x, y;
};

double distance(const Pos& a, const Pos& b) {
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    return sqrt(dx * dx + dy * dy);
}

constexpr double D_INF = 1e20;

using Pid = pair<int, double>;
using Pdi = pair<double, int>;
using Graph = vector<vector<Pid>>;

void solve() {
    ll N, M, X, Y;
    cin >> N >> M >> X >> Y;
    --X, --Y;
    vector<Pos> poss(N);
    for (ll i = 0; i < N; i++) {
        cin >> poss[i].x >> poss[i].y;
    }

    Graph g(N);

    for (ll i = 0; i < M; i++) {
        ll a, b;
        cin >> a >> b;
        --a, --b;
        double c = distance(poss[a], poss[b]);
        g[a].emplace_back(b, c);
        g[b].emplace_back(a, c);
    }

    vector<double> dist(N, D_INF);
    dist[X] = 0.0;
    priority_queue<Pdi, vector<Pdi>, greater<Pdi>> q;
    q.emplace(0.0, X);
    while (!q.empty()) {
        auto [cost, idx] = q.top();
        q.pop();
        if (dist[idx] < cost) continue;
        for (const auto& [to, c] : g[idx]) {
            double ncost = cost + c;
            if (ncost >= dist[to]) continue;
            dist[to] = ncost;
            q.emplace(ncost, to);
        }
    }

    cout << setprecision(20) << dist[Y] << "\n";
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

int main() {
#ifdef FASTIO
    cin.tie(0), cout.tie(0);
    ios::sync_with_stdio(false);
#endif
#ifdef FILEINPUT
    ifstream ifs("./in_out/input.txt");
    cin.rdbuf(ifs.rdbuf());
#endif
#ifdef FILEOUTPUT
    ofstream ofs("./in_out/output.txt");
    cout.rdbuf(ofs.rdbuf());
#endif
    solve();
    cout << flush;
    return 0;
}