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

using lnt = long long;
using Real = long double;

#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define REP(i, n) for(lnt i=0;i<(n);++i)
#define RANGE(i, a, b) for(lnt i=(a);i<(b);++i)
#define RREP(i, n) for(lnt i=(n)-1;i>= 0;--i)

#define ln '\n'
#define pb push_back
#define eb emplace_back
#define pque priority_queue
#define umap unordered_map
#define uset unordered_set
#define dcout cout<<fixed<<setprecision(20)
#define summon_tourist cin.tie(0);ios::sync_with_stdio(false)

constexpr int dx[]={1,0,-1,0,1,1,-1,-1}, dy[]={0,-1,0,1,1,-1,1,-1};
constexpr Real eps = 1e-9; const Real pi = acosl(-1);
constexpr lnt BIG = INT_MAX/10, BBIG = LLONG_MAX/10;

template<class T> inline T GCD(T a,T b){T c;while(b!=0){c=a%b;a=b;b=c;}return a;}
template<class T> inline T LCM(T a,T b){T c=GCD(a,b);a/=c;return a*b;}
template<class T> inline T nCr(T a,T b){T i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
template<class T> inline T nHr(T a,T b){return nCr(a+b-1,b);}
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;}

using pint = pair<int, int>; using plnt = pair<lnt, lnt>;
using vint = vector<int>; using vlnt = vector<lnt>;
constexpr lnt MOD = 1e9+7;

struct edge {int to; Real cost;};

int main(){
	summon_tourist;

	int N, M, X, Y; cin >> N >> M >> X >> Y;
	X--; Y--;
	vector<Real> p(N), q(N);
	vector<vector<edge>> G(N);
	REP(i, N) cin >> p[i] >> q[i];

	REP(i, M){
		int u, v; cin >> u >> v;
		u--; v--;
		Real dis = sqrtl( powl(p[u]-p[v], 2) + powl(q[u]-q[v], 2) );
		G[u].pb({v, dis});
		G[v].pb({u, dis});
	}

	using PA = pair<Real, int>;
	vector<Real> dist(N, 1e9); dist[X] = 0.0;
	pque<PA, vector<PA>, greater<PA>> que;
	que.push({0.0, X});

	while(!que.empty()){
		PA pa = que.top(); que.pop();
		int pos = pa.second;
		if(dist[pos] < pa.first) continue;
		for(auto e: G[pos]){
			if(dist[pos] + e.cost < dist[e.to]){
				dist[e.to] = dist[pos] + e.cost;
				que.push({dist[e.to], e.to});
			}
		}
	}

	dcout << dist[Y] << ln;
}