#include"bits/stdc++.h"
using namespace std;
#define REP(k,m,n) for(int (k)=(m);(k)<(n);(k)++)
#define rep(i,n) REP((i),0,(n))
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using tp3 = tuple<int, int, int>;
using Mat = vector<vector<ll>>;
constexpr int INF = 1 << 28;
constexpr ll INFL = 1ll << 60;
constexpr int dh[4] = { 0,1,0,-1 };
constexpr int dw[4] = { -1,0,1,0 };
bool isin(const int H, const int W, const int h, const int w) {
    return 0 <= h && h < H && 0 <= w && w < W;
}
// ============ template finished ============
using pdd = pair<double, double>;
using pdi = pair<double, int>;
double dist(const vector<pdd>& pq, const int from, const int to) {
    pdd d = { pq[to].first - pq[from].first,pq[to].second - pq[from].second };
    return sqrt(d.first*d.first + d.second*d.second);
}

int main()
{
    int N, M, X, Y;
    cin >> N >> M >> X >> Y;
    X--; Y--;
    vector<pdd> poss(N);
    vector<vector<int>> edges(N);
    rep(i, N)cin >> poss[i].first >> poss[i].second;
    rep(i, M) {
        int P, Q;
        cin >> P >> Q;
        P--; Q--;
        edges[P].push_back(Q);
        edges[Q].push_back(P);
    }
    vector<double> ds(N, INFL);
    priority_queue<pdi, vector<pdi>, greater<pdi>> pq;
    ds[X] = 0;
    pq.push({ 0,X });
    while (!pq.empty()) {
        double d;
        int now;
        tie(d, now) = pq.top(); pq.pop();
        for (auto next : edges[now]) {
            double nd = d + dist(poss, now, next);
            if (nd < ds[next]) {
                ds[next] = nd;
                pq.push({ nd,next });
            }
        }
    }
    cout << fixed << setprecision(12) << ds[Y] << endl;
    return 0;
}