#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <numeric>
#include <cmath>
#include <iomanip> //cout << fixed << setprecision(15) << << endl;
#include <cassert>
#include <limits>
//#include "atcoder/all"

using namespace std;
//using namespace atcoder;

#define ll long long int
#define pb push_back
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for(int i=1;i<=(n);i++)
//#define P pair<int,int>

int mx8[] = {0,0,1,-1,-1,1,-1,1};
int my8[] = {-1,1,0,0,-1,-1,1,1};
int mx4[] = {1,-1,0,0};
int my4[] = {0,0,-1,1};

template<typename T>
class Graph
{
public:
    struct Edge
    {
        int to;
        T cost;
    };
    struct edge
    {
        int from;
        int to;
    };
    vector<vector<Edge>> g;
    int n;
    Graph(int n)
    {
        g.resize(n);
    }

    void Add(int from, int to, T cost)
    {
        g[from].push_back({to,cost});
        g[to].push_back({from,cost});
    }

};

template<typename T>
vector<T> dijkstra(Graph<T> G, int start)
{
    using P = pair<T,int>;
    vector<T> dist(G.n, numeric_limits<T>::max());
    priority_queue<P,vector<P>,greater<P>> pq;
    dist[start] = 0;
    pq.push({dist[start],start});
    while(!pq.empty())
    {
        T COST = pq.top().first;
        int v = pq.top().second;
        pq.pop();

        if(dist[v] < COST)
        {
            continue;
        }
        for(auto e : G.g[v])
        {
            int j = e.to;
            T c = e.cost;
            if(dist[j] > dist[v] + c)
            {
                dist[j] = dist[v] + c;
                pq.push({dist[j],j});
            }
        }
    }
    return dist;
}


int main(){
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    --x; --y;
    vector<double> p(n),q(n);
    rep(i,n) cin >> p[i] >> q[i];

    Graph<double> G(n);
    rep(i,m){
        int P, Q; cin >> P >> Q;
        P--; Q--;
        double Co = sqrt(pow((p[P]-p[Q]),2) + pow((q[P]-q[Q]),2));
        G.Add(P,Q,Co);
    }
    vector<double> ans;
    ans = dijkstra(G,x);
    cout << fixed << setprecision(10) << ans[y] << endl;
}