#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;

template<typename T> using pq = priority_queue<T, vector<T>, greater<T>>;
 
int main(){
 
    long long N, M, start, goal, from, P, Q;
    cin >> N >> M >> start >> goal;
    start--; goal--;
    long double alt, d;
    vector<long double> X(N), Y(N);
    for (int i=0; i<N; i++) cin >> X[i] >> Y[i];

    pq<pair<long double, long long>> que;
    vector<vector<pair<long long, long double>>> E(N);
    vector<long double> dist(N, 1e18);
    vector<bool> visit(N);
 
    for (int i=0; i < M; i++){
        cin >> P >> Q; P--; Q--;
        d = sqrt((X[P]-X[Q])*(X[P]-X[Q])+(Y[P]-Y[Q])*(Y[P]-Y[Q]));
        E[P].push_back({Q, d});
        E[Q].push_back({P, d});
    }
 
    dist[start] = 0;
    que.push({0, start});
 
    while(!que.empty()){
        tie(d, from) = que.top();
        que.pop();
        if (visit[from]) continue;
        visit[from] = 1;
        for (auto [to, C] : E[from]){
            alt = d + C;
            if (alt < dist[to]){
                dist[to] = alt;
                que.push({dist[to], to});
            }
        }
    }

    cout << setprecision(18) << dist[goal] << endl;
 
    return 0;
}