#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define INF 1000000000
#define mod 1000000007
using ll=long long;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

template<typename T>
vector<T> dijkstra(int s,vector<vector<pair<int,T>>> &G){
    const T TINF=numeric_limits<T>::max();
    using P=pair<T,int>;
    int n=G.size();
    vector<T> d(n,TINF);
    vector<int> b(n,-1);//previous point
    priority_queue<P,vector<P>,greater<P>> q;
    d[s]=0;
    q.emplace(d[s],s);
    while(!q.empty()){
        P p=q.top();q.pop();
        int v=p.second;
        if(d[v]<p.first) continue;
        for(auto& e:G[v]){
            int u=e.first;
            T c=e.second;
            if(d[u]>d[v]+c){
                d[u]=d[v]+c;
                b[u]=v;
                q.emplace(d[u],u);
            }
        }
    }
    return d;
}


signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    cout<<fixed<<setprecision(12);

    int n,m;cin>>n>>m;
    int st,gl;cin>>st>>gl;st--,gl--;

    vector<vector<pair<int,double>>> g(n);

    double x[n],y[n];
    rep(i,n){
        cin>>x[i]>>y[i];
    }

    rep(i,m){
        int u,v;cin>>u>>v;u--,v--;
        g[u].push_back({v,sqrt((x[u]-x[v])*(x[u]-x[v])+(y[u]-y[v])*(y[u]-y[v]))});
        g[v].push_back({u,sqrt((x[u]-x[v])*(x[u]-x[v])+(y[u]-y[v])*(y[u]-y[v]))});
    }

    auto dis=dijkstra(st,g);
    cout<<dis[gl]<<endl;
    return 0;
}