#include <bits/stdc++.h>
using namespace std;

// #define int long long
#define rep(i, n) for (long long i = (long long)(0); i < (long long)(n); ++i)
#define reps(i, n) for (long long i = (long long)(1); i <= (long long)(n); ++i)
#define rrep(i, n) for (long long i = ((long long)(n)-1); i >= 0; i--)
#define rreps(i, n) for (long long i = ((long long)(n)); i > 0; i--)
#define irep(i, m, n) for (long long i = (long long)(m); i < (long long)(n); ++i)
#define ireps(i, m, n) for (long long i = (long long)(m); i <= (long long)(n); ++i)
#define SORT(v, n) sort(v, v + n);
#define REVERSE(v, n) reverse(v, v+n);
#define vsort(v) sort(v.begin(), v.end());
#define all(v) v.begin(), v.end()
#define mp(n, m) make_pair(n, m);
#define cout(d) cout<<d<<endl;
#define coutd(d) cout<<std::setprecision(10)<<d<<endl;
#define cinline(n) getline(cin,n);
#define replace_all(s, b, a) replace(s.begin(),s.end(), b, a);
#define PI (acos(-1))
#define FILL(v, n, x) fill(v, v + n, x);
#define sz(x) long long(x.size())

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vs = vector<string>;
using vpll = vector<pair<ll, ll>>;
using tll = tuple<ll,ll,ll>;
using vtll = vector<tuple<ll,ll,ll>>;
using vb = vector<bool>;

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 INF = 1e9;
const ll MOD = 10000;
const ll LINF = 1e18;

vll G[200100];
double dist[200100];

signed main()
{
  cin.tie( 0 ); ios::sync_with_stdio( false );
  
  ll n,m; cin>>n>>m;
  ll x,y; cin>>x>>y; x--,y--;
  vpll P(n);
  rep(i,n){
    ll a,b; cin>>a>>b;
    P[i]={a,b};
  }
  
  rep(i,m){
    ll a,b; cin>>a>>b; a--,b--;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  
  fill(dist,dist+n,LINF);
  
  priority_queue<pair<double,ll>, vector<pair<double,ll>>, greater<pair<double,ll>>> q;
  q.emplace(0,x);
  dist[x]=0;
  
  while(!q.empty()){
    auto p=q.top(); q.pop();
    ll v=p.second; double c=p.first;
    if(dist[v]<c) continue;
    for(auto nv: G[v]){
      double span=sqrt((P[v].first-P[nv].first)*(P[v].first-P[nv].first)+(P[v].second-P[nv].second)*(P[v].second-P[nv].second));
      if(chmin(dist[nv],dist[v]+span)){
        q.emplace(dist[nv],nv);
      }
    }
  }
  
  cout<<std::setprecision(10)<<dist[y]<<endl;
  
}