#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(i,n) for (int i = 0; i < (n); ++i)
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
const ll INF=1LL<<60;
const int inf=(1<<30)-1;
const int mod=1e9+7;
int dx[8]={1,0,-1,0,-1,-1,1,1};
int dy[8]={0,1,0,-1,-1,1,-1,1};
const int nmax=200005;
vector<vector<pair<ll,ld>>> g(nmax);
ld d[nmax];
void dijkstra(ll s){
  priority_queue<pair<ll,ld>,vector<pair<ll,ld>>,greater<pair<ll,ld>>> pq;
  fill(d,d+nmax,inf);
  d[s]=0;
  pq.push(make_pair(0,s));
  while(!pq.empty()){
    pair<ll,ll> p=pq.top();
    pq.pop();
    ll v=p.second;
    if(d[v]<p.first){
      continue;
    }
    for(auto x:g[v]){
      if(d[x.first]>d[v]+x.second){
        d[x.first]=d[v]+x.second;
        pq.push(make_pair(d[x.first],x.first));
      }
    }
  }
}
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;cin >> n >> m;
    int x,y;cin >> x >> y;
    x--,y--;
    vector<int> p(n),q(n);
    rep(i,n){
        cin >> p[i] >> q[i];
    }
    rep(i,m){
        int u,v;cin >> u >> v;
        u--,v--;
        double dis=sqrt((p[u]-p[v])*(p[u]-p[v])+(q[u]-q[v])*(q[u]-q[v]));
        g[u].push_back({v,dis});
        g[v].push_back({u,dis});
    }
    dijkstra(x);
    cout << fixed << setprecision(10) << d[y] << endl;
}