#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N, M, S, T;
    cin >> N >> M >> S >> T;
    --S, --T;
    vector<complex<double>> ps;
    for(int i = 0; i < N; ++i){
        double x, y;
        cin >> x >> y;
        ps.emplace_back(x, y);
    }
    vector<vector<pair<int, double>>> graph(N);
    for(int i = 0; i < M; ++i){
        int u, v;
        cin >> u >> v;
        --u, --v;
        double d = abs(ps[u] - ps[v]);
        graph[u].emplace_back(v, d);
        graph[v].emplace_back(u, d);
    }

    vector<double> dist(N, 1e+30);
    using Data = pair<double, int>;
    priority_queue<Data, vector<Data>, greater<Data>> que;
    dist[S] = 0.0;
    que.emplace(0, S);
    while(!que.empty()){
        auto [d, from] = que.top();
        que.pop();
        if(dist[from] > d)  continue;
        for(auto [to, cost] : graph[from]){
            if(chmin(dist[to], dist[from] + cost)){
                que.emplace(dist[to], to);
            }
        }
    }

    cout << fixed << setprecision(15);
    cout << dist[T] << endl;

    return 0;
}