#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define Z class
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}void pr(){ln;}
template<Z A,Z...B>void pr(const A &a,const B&...b){cout<<a<<(sizeof...(b)?" ":"");pr(b...);}
template<Z A>void PR(A a,ll n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[8]={-1,0,1,0,-1,-1,1,1},dy[8]={0,1,0,-1,-1,1,1,-1};
typedef pair<double,double> P;

double D(P a,P b) {
  return sqrt((a.F-b.F)*(a.F-b.F)+(a.S-b.S)*(a.S-b.S));
}

void Main() {
  ll n,m,s,t;
  cin >> n >> m >> s >> t;
  s--,t--;
  P a[n];
  rep(i,n) cin >> a[i].F >> a[i].S;
  vector<ll> v[n];
  rep(i,m) {
    ll x,y;
    cin >> x >> y;
    x--,y--;
    v[x].pb(y);
    v[y].pb(x);
  }
  priority_queue<P,vector<P>,greater<P> > que;
  que.push(P(0,s));
  double d[n];
  fill(d,d+n,MAXL);
  d[s]=0;
  while(!que.empty()) {
    P p=que.top();que.pop();
    double c=p.F;
    ll x=p.S;
    if(d[x]<c) continue;
    rep(i,v[x].size()) {
      ll y=v[x][i];
      double cc=c+D(a[x],a[y]);
      if(d[y]>cc) {
        d[y]=cc;
        que.push(P(cc,y));
      }
    }
  }
  pd(d[t]);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}