#include <bits/stdc++.h>  // clang-format off
using Int = long long;
#define REP_(i, a_, b_, a, b, ...) for (Int i = (a), lim##i = (b); i < lim##i; i++)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
struct SetupIO { SetupIO() { std::cin.tie(nullptr), std::ios::sync_with_stdio(false), std::cout << std::fixed << std::setprecision(13); } } setup_io;
#ifndef dump
#define dump(...)
#endif  // clang-format on

/**
 *    author:  knshnb
 *    created: Fri May 29 22:12:23 JST 2020
 **/

template <class T, bool directed = true> struct Dijkstra {
    struct Edge {
        int to;
        T cost;
    };
    std::vector<std::vector<Edge>> g;
    Dijkstra(int n) : g(n) {}
    void add_edge(int u, int v, T cost) {
        g[u].push_back({v, cost});
        if (!directed) g[v].push_back({u, cost});
    }
    std::vector<T> run(int s) {
        std::vector<T> dist(g.size(), std::numeric_limits<T>::max() / 2);
        // {d, v}
        std::priority_queue<std::pair<T, int>, std::vector<std::pair<T, int>>, std::greater<std::pair<T, int>>> q;
        q.push({0, s});
        while (!q.empty()) {
            std::pair<T, int> p = q.top();
            q.pop();
            int v = p.second;
            if (dist[v] <= p.first) continue;
            dist[v] = p.first;
            for (const Edge& e : g[v]) {
                if (dist[e.to] <= p.first + e.cost) continue;  // 定数倍枝刈り
                q.emplace(p.first + e.cost, e.to);
            }
        }
        return dist;
    }
};

signed main() {
    Int n, m, x, y;
    std::cin >> n >> m >> x >> y;
    x--, y--;
    Dijkstra<double, false> g(n);
    std::vector<Int> p(n), q(n);
    REP(i, n) std::cin >> p[i] >> q[i];
    REP(i, m) {
        Int u, v;
        std::cin >> u >> v;
        u--, v--;
        double dx = p[u] - p[v], dy = q[u] - q[v];
        g.add_edge(u, v, sqrt(dx * dx + dy * dy));
    }
    std::cout << g.run(x)[y] << std::endl;
}