#define CPP17
#include <limits>
#include <initializer_list>
#include <utility>
#include <bitset>
#include <tuple>
#include <type_traits>
#include <functional>
#include <string>
#include <array>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <iterator>
#include <algorithm>
#include <complex>
#include <random>
#include <numeric>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <regex>
#include <cassert>
#include <cstddef>
#ifdef CPP17
#include <variant>
#endif

// Yay!!
#define endl codeforces

// macros for iterator
#define ALL(v) std::begin(v), std::end(v)
#define ALLR(v) std::rbegin(v), std::rend(v)

// alias
using ll = std::int64_t;
using ull = std::uint64_t;
using pii = std::pair<int, int>;
using tii = std::tuple<int, int, int>;
using pll = std::pair<ll, ll>;
using tll = std::tuple<ll, ll, ll>;
template <typename T> using vec = std::vector<T>;
template <typename T> using vvec = vec<vec<T>>;

// variadic min/max
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }

// variadic chmin/chmax
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }

// multi demension array
template <typename T, std::size_t Head, std::size_t... Tail> struct multi_dim_array { using type = std::array<typename multi_dim_array<T, Tail...>::type, Head>; };
template <typename T, std::size_t Head> struct multi_dim_array<T, Head> { using type = std::array<T, Head>; };
template <typename T, std::size_t... Args> using mdarray = typename multi_dim_array<T, Args...>::type;

#ifdef CPP17
// fill container
template <typename T, typename F, typename... Args> 
void fill_seq(T &t, F f, Args... args) { if constexpr (std::is_invocable<F, Args...>::value) { t = f(args...); } else { for (ssize_t i = 0; i < t.size(); i++) fill_seq(t[i], f, args..., i); } }
#endif

// make multi dimension vector
template <typename T> vec<T> make_v(ssize_t sz) { return vec<T>(sz); }
template <typename T, typename... Tail> auto make_v(ssize_t hs, Tail&&... ts) { auto v = std::move(make_v<T>(std::forward<Tail>(ts)...)); return vec<decltype(v)>(hs, v); }

// init
namespace init__ { 
struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; 
}


namespace tree {

struct UnionFind {
    vec<ll> rank, par;
    vec<ssize_t> sz;

    UnionFind(ll n) : rank(n), par(n), sz(n) {
        init();
    }

    void init() {
        std::fill(ALL(rank), 1);
        std::iota(ALL(par), 0);
        std::fill(ALL(sz), 1);
    }

    ll find(ll n) {
        return (n == par[n] ? n : par[n] = find(par[n]));
    }

    bool unit(ll x, ll y) {
        ll px = find(x), py = find(y);
        if (px == py) return false;
        if (rank[px] < rank[py]) std::swap(px, py);
        par[py] = px;
        rank[px] += (rank[px] == rank[py]);
        sz[px] += sz[py];
        return true;
    }

    bool same(ll x, ll y) {
        return find(x) == find(y);
    }

    ssize_t size(ll n) {
        return sz[find(n)];
    }
};

}

int main() {
    using ld = long double;
    using pdd = std::pair<ld, ld>;
    using pld = std::pair<ll, ld>;
    using pdl = std::pair<ld, ll>;
    ll n, m, x, y;
    std::cin >> n >> m;
    std::cin >> x >> y;
    x--; y--;
    vec<pdd> vn(n);
    for (auto &&e : vn) {
        ld a, b;
        std::cin >> a >> b;
        e = pll(a, b);
    }

    auto pow2 = [](ld a) { return a * a; };
    auto dist = [&](pdd p, pdd q) {
        auto [ a, b ] = p;
        auto [ c, d ] = q;
        return std::sqrt(pow2(a - c) + pow2(b - d));
    };

    vvec<pld> edges(n);
    for (ll i = 0; i < m; i++) {
        ll a, b;
        std::cin >> a >> b;
        a--; b--;
        auto d = dist(vn[a], vn[b]);
        edges[a].emplace_back(b, d);
        edges[b].emplace_back(a, d);
    }

    const ld inf = std::numeric_limits<ld>::max() / 3;
    vec<ld> dists(n, inf);
    dists[x] = 0;
    std::priority_queue<pdl, vec<pdl>, std::greater<pdl>> pq;
    pq.emplace(0, x);
    while (pq.size()) {
        auto [ d, cur ] = pq.top();
        pq.pop();
        if (dists[cur] < d) continue;
        for (auto &&e : edges[cur]) {
            auto [ nxt, cost ] = e;
            auto nd = d + cost;
            if (dists[nxt] <= nd) continue;
            dists[nxt] = nd;
            pq.emplace(nd, nxt);
        }
    }

    std::cout << dists[y] << "\n";
    return 0;
}