#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define rep(i,n) for(ll i=0;i<(n);i++)
#define pll pair<ll,ll>
#define pq priority_queue
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance(c.begin(),lower_bound(all(c),x))
#define ub(c,x) distance(c.begin(),upper_bound(all(c),x))

using namespace std;

template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

const ll mod=1e9+7;

vector<pair<ll,long double>> to[200005];

const ll INF=1e10+100;
const ll white=0; //未探索
const ll gray=1; //探索中
const ll black=2; //探索済み

ll n,x;
vector<long double> d;

void dijkstra(){
    priority_queue<pll> PQ;
    vector<ll> color(n);
    rep(i,n){
        d[i]=INF;
        color[i]=white;
    }
    d[x]=0;
    PQ.push(make_pair((long double)0.0,x));
    color[x]=gray;
    while(!PQ.empty()){
        pll f=PQ.top();
        PQ.pop();
        ll u=f.second;
        color[u]=black;
        if(d[u]<f.first*(-1)) continue; //d[u]は正。
        for(ll j=0;j<to[u].size();j++){
            ll v=to[u][j].first;
            if(color[v]==black) continue;
            if(d[v]>d[u]+to[u][j].second){
                d[v]=d[u]+to[u][j].second;
                PQ.push(make_pair(d[v]*(-1),v));
                color[v]=gray;
            }
        }
    }
    /*rep(i,n){
        if(d[i]==INF){
            cout << "INF" << endl;
        }
        else{
            cout << d[i] << endl;
        }
    }*/
}

int main()
{
    ll m;
    cin >> n >> m;
    ll y;
    cin >> x >> y;
    x--; y--;
    d.resize(n);
    vector<pair<long double,long double>> p(n);
    rep(i,n){
        cin >> p[i].fi >> p[i].se;
    }
    rep(i,m){
        ll s,t;
        cin >> s >> t;
        s--; t--;
        ll dx=p[s].fi-p[t].fi;
        ll dy=p[s].se-p[t].se;
        long double dist=sqrt(dx*dx+dy*dy);
        to[s].push_back(make_pair(t,dist));
        to[t].push_back(make_pair(s,dist));
    }
    dijkstra();
    cout << fixed << setprecision(10);
    cout << d[y] << endl;
    return 0;
}