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

int main() {
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    x--; y--;
    vector<int> a(n), b(n);
    for (int i = 0; i < n; i++) {
        cin >> a.at(i) >> b.at(i);
    }
    vector<vector<pair<int, double>>> to(n);
    for (int i = 0; i < m; i++) {
        int p, q;
        cin >> p >> q;
        p--; q--;
        int dx = a.at(p) - a.at(q), dy = b.at(p) - b.at(q);
        to.at(p).emplace_back(q, sqrt(dx * dx + dy * dy));
        to.at(q).emplace_back(p, sqrt(dx * dx + dy * dy));
    }
    vector<double> d(n, 1e9);
    d.at(x) = 0;
    priority_queue<pair<double, int>> que;
    que.emplace(0, x);
    while (!que.empty()) {
        auto t = que.top();
        double d0 = -t.first;
        int v = t.second;
        que.pop();
        if (v == y) break;
        if (d.at(v) < d0) continue;
        for (auto next : to.at(v)) {
            if (d.at(next.first) <= d0 + next.second) continue;
            d.at(next.first) = d0 + next.second;
            que.emplace(-d.at(next.first), next.first);
        }
    }
    cout << setprecision(17) << d.at(y) << endl;
}