/*** author: yuji9511 ***/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using lpair = pair<double, ll>;
const ll MOD = 1e9+7;
const ll INF = 1e18;
#define rep(i,m,n) for(ll i=(m);i<(n);i++)
#define rrep(i,m,n) for(ll i=(m);i>=(n);i--)
#define printa(x,n) for(ll i=0;i<n;i++){cout<<(x[i])<<" \n"[i==n-1];};
void print() {}
template <class H,class... T>
void print(H&& h, T&&... t){cout<<h<<" \n"[sizeof...(t)==0];print(forward<T>(t)...);}
vector< pair<ll, double> > tree[200010];
void solve(){
    ll N,M;
    cin >> N >> M;
    ll X,Y;
    cin >> X >> Y;
    X--; Y--;
    double p[200010], q[200020];
    rep(i,0,N) cin >> p[i] >> q[i];
    ll u[200010], v[200010];
    rep(i,0,M){
        cin >> u[i] >> v[i];
        u[i]--; v[i]--;
        double d = sqrt((p[u[i]] - p[v[i]]) * (p[u[i]] - p[v[i]]) + (q[u[i]] - q[v[i]]) * (q[u[i]] - q[v[i]]));
        tree[u[i]].push_back({v[i], d});
        tree[v[i]].push_back({u[i], d});

    }
    
    priority_queue pq([](lpair l1, lpair l2){return l1 > l2;}, vector<lpair>());
    
    // priority_queue<lpair, vector<lpair> ,compare > pq;
    double dist[100010] = {};
    rep(i,0,N) dist[i] = INF;
    dist[X] = 0.0;
    pq.push({0.0,X});
    while(!pq.empty()){
        lpair l1 = pq.top();
        pq.pop();
        if(dist[l1.second] < l1.first) continue;
        for(auto &e: tree[l1.second]){
            if(dist[e.first] > dist[l1.second] + e.second){
                dist[e.first] = dist[l1.second] + e.second;
                pq.push(make_pair(dist[e.first], e.first));
            }
        }
    }
    cout << setprecision(10) << dist[Y] << endl;

}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}